How to call a method from a different class in java and how to fix" non static method cannot be referenced from a static content" error?

I want to call the homeValue method from the house class to the method valOfHouse in the HouseHelper class. I keep getting an error "non static method cannot be referenced from a static content". How can i fix this code? I can only make changes to the HouseHelper class.

public class House 
{ 
public House (String _location, String _realtor, String _color, int _rooms, int _price, int _size, int _year) 
{ 
this.location = _location; 
this.realtor = _realtor; 
this.color = _color; 
this.rooms = _rooms; 
this.price = _price; 
this.size = _size; 
this.year = _year; 
} 
public int homeValue() 
{ 
Calendar calendar= Calendar.getInstance(); 
int ageOfHome = calendar.get(Calendar.YEAR) - year; 
if (ageOfHome <= 0) 
ageOfHome=1; 
int older = ageOfHome * 12000; 
int new = ageOfHome * 10000; 
int val = price; 
if (price > older) 
currentVal -= age * 1550; 
else if (price < new) 
val -= ageOfHome * 1300; 
else 
val -= ageOfHome * 1400; 
return val; 
} 

public class HouseHelper 
{ 


 public int valOfHouse() 
{ int total = 0;
  total = House.homeValue();

 return total; // non static method cannot be referenced from a static content
 }