Local Variable named ... is already defined in this scope

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C#

Visual-Studio

Hi! First, I am SO sorry for my long names, I've been overly descriptive in this assignment because I'm still pretty new, and this has a lot going on.

The problem is this: I need my "calculate" button to calculate my equations, then highlight the label with the smaller total. I used the same variable name twice, as I need it twice, but it seems like I told it 1+1=2, then told it 1+1=4, so I understand WHY I have the error. I just don't know how to fix it. I tried brackets {} but it still gives the error because it's still part of the parent scope, and if I move one out of it, the button won't do both things.

The part that is wrong specifically is this:

//HIGHLIGHTING highlight lesser cost in green

            decimal calc5YrTotal1 = Convert.ToInt32(label5YearTotalCostAnswerCar1.Text);
            decimal calc5YrTotal2 = Convert.ToInt32(label5YearTotalCostAnswerCar2.Text);
            if (calc5YrTotal1 < calc5YrTotal2)
            label5YearTotalCostAnswerCar1.BackColor = Color.Green;
            else
            label5YearTotalCostAnswerCar2.BackColor = Color.Green;

calc1YearGasCar1 and calc1YearGasCar2 are the variables used twice. 

********UPDATE********************

I tried renaming them, and I got another error. 
I tried: 

decimal calc5YrTotal1 = Convert.ToInt32(label5YearTotalCostAnswerCar1.Text);
decimal calc5YrTotal2 = Convert.ToInt32(label5YearTotalCostAnswerCar2.Text);
if (calc1YearGasCar1 < calc1YearGasCar2)
label5YearTotalCostAnswerCar1.BackColor = Color.Green;
else
label5YearTotalCostAnswerCar2.BackColor = Color.Green;

I got this error:

An unhandled exception of type 'System.FormatException' occurred in mscorlib.dll

Additional information: Input string was not in a correct format.

*****************************************************************************

My ENTIRE code is this:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace CarCostComparison___AmyCollins
{
    public partial class FormCarCostComparison : Form
    {
        public FormCarCostComparison()
        {
            InitializeComponent();
        }

        private void label3_Click(object sender, EventArgs e)
        {

        }

        private void FormCarCostComparison_Load(object sender, EventArgs e)
        {
            //Author: Amy C


        }

        private void buttonCalculate_Click(object sender, EventArgs e)
        {

            //Constants assumed price of gas and miles driven a year

            const decimal constPriceGas = 3.5m;
            const decimal constMilesDriven = 12000;

            //Variables user entered for car 1 and 2

            decimal userEnteredMPGCar1 = 0;
            decimal userEnteredInsuranceCar1 = 0;
            decimal userEnteredPurchasePriceCar1 = 0;
            decimal userEnteredRepairCar1 = 0;

            decimal userEnteredMPGCar2 = 0;
            decimal userEnteredPurchasePriceCar2 = 0;
            decimal userEnteredRepairCar2 = 0;
            decimal userEnteredInsuranceCar2 = 0;

            //Variables calculations

            decimal calc1YearGasCar1 = 0;
            decimal calc5YearCostCar1 = 0;

            decimal calc1YearGasCar2 = 0;
            decimal calc5YearCostCar2 = 0;

            //Input convert

            userEnteredMPGCar1 = decimal.Parse(textBoxMPG1.Text);
            userEnteredInsuranceCar1 = decimal.Parse(textBoxInsuranceCost1.Text);
            userEnteredPurchasePriceCar1 = decimal.Parse(textBoxPurchasePrice1.Text);
            userEnteredRepairCar1 = decimal.Parse(textBoxRepairCost1.Text);

            userEnteredMPGCar2 = decimal.Parse(textBoxMPG2.Text);
            userEnteredInsuranceCar2 = decimal.Parse(textBoxInsuranceCost2.Text);
            userEnteredPurchasePriceCar2 = decimal.Parse(textBoxPurchasePrice2.Text);
            userEnteredRepairCar2 = decimal.Parse(textBoxRepairCost2.Text);

            //Processing calculations 5 year total cost and 1 year fuel cost

            calc1YearGasCar1 = (constMilesDriven / userEnteredMPGCar1 * constPriceGas);

            calc5YearCostCar1 = (userEnteredPurchasePriceCar1 + (calc1YearGasCar1 * 5) + (userEnteredInsuranceCar1 * 5) + (userEnteredRepairCar1 * 5));


            calc1YearGasCar2 = (constMilesDriven / userEnteredMPGCar2 * constPriceGas);

            calc5YearCostCar2 = (userEnteredPurchasePriceCar2 + (calc1YearGasCar2 * 5) + (userEnteredInsuranceCar2 * 5) + (userEnteredRepairCar2 * 5));

            //Output convert 

            label1YearFuelAnswerCar1.Text = calc1YearGasCar1.ToString();
            label5YearTotalCostAnswerCar1.Text = calc5YearCostCar1.ToString();

            label1YearFuelAnswerCar2.Text = calc1YearGasCar2.ToString();
            label5YearTotalCostAnswerCar2.Text = calc5YearCostCar2.ToString();

             //HIGHLIGHTING highlight lesser cost in green

                int calc1YearGasCar1 = Convert.ToInt32(label5YearTotalCostAnswerCar1.Text);
                int calc1YearGasCar2 = Convert.ToInt32(label5YearTotalCostAnswerCar2.Text);
                if (calc1YearGasCar1 < calc1YearGasCar2)
                    label5YearTotalCostAnswerCar1.BackColor = Color.Green;
                else
                    label5YearTotalCostAnswerCar2.BackColor = Color.Green;
            




        }

        private void textBoxMPG1_TextChanged(object sender, EventArgs e)
        {

        }

        private void textBoxMake2_TextChanged(object sender, EventArgs e)
        {

        }

        private void buttonClear_Click(object sender, EventArgs e)
        {
            //Clear Button

            textBoxMake1.Text = "";
            textBoxModel1.Text = "";
            textBoxYear1.Text = "";
            textBoxMPG1.Text = "";
            textBoxPurchasePrice1.Text = "";
            textBoxRepairCost1.Text = "";
            textBoxInsuranceCost1.Text = "";
            label1YearFuelAnswerCar1.Text = "";
            label5YearTotalCostAnswerCar1.Text = "";

            textBoxMake2.Text = "";
            textBoxModel2.Text = "";
            textBoxYear2.Text = "";
            textBoxMPG2.Text = "";
            textBoxPurchasePrice2.Text = "";
            textBoxRepairCost2.Text = "";
            textBoxInsuranceCost2.Text = "";
            label1YearFuelAnswerCar2.Text = "";
            label5YearTotalCostAnswerCar2.Text = "";

            //Note to self (placeholder)
        }

        private void label5YearTotalCost_Click(object sender, EventArgs e)
        {

        }
    }
}

(Also, knowing how to clear all the boxes in an easier way would be great, but I'm just worried about the error for now)

Any help is much appreciated!!

Amy