access to a parent class of parent class variable?

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Java

> hi.
I am doing exercise c-2.5 of java data structure book. but I have a problem.
question : write a program that consist of three classes, A, B, C, such that B extends A and C extends B. Each class should define an instance variable named "x". Describe a way for a method in C to access and set A's version of x to a given value, without changing B or C's version.
I wrote these three classes but in method setX() there is errors.please guide me ...

public class A {

	public int x;
	public A(){
		x=0;
	}
}


public class B extends A{

	private int x;
	public B()
	{
		x=0;
		
	}
}


public class C extends B{

	public int x;
	public C(){
		x=0;
	}
	public void setX(int a){
	
		super.x=a;
	}
}