Introductory Java Student assigning an existing variable to another -

my apologies if seems simple question, new computer science student , question has me stumped.

suppose car variable billscar exists , refers car object. write statement assigns billscar's unused capacity double variable amtleft.

below source code:

  public class car{  // car attributes  string make; // manufacturer  double fuelcapacity;  double fuelamount;   // car constructor    public car(string what, double cap, double amt){   make = what;   fuelcapacity = cap;   fuelamount = amt;  }  // car methods   public string getmake(){   return make;  }   public double getcapacity(){   return fuelcapacity;  }   public double getfuel(){   return fuelamount; }   public void setfuel(double amt){     fuelamount = amt;  }     public double unusedcap(){     return (fuelcapacity - fuelamount);  }    } 

the answer block begins double amtleft = ; proper way of assigning billscar unused capacity (a varible not know) double variable amtleft?

change unusedcap() this?

public double unusedcap() {             double fuelleft=(fuelcapacity - fuelamount);             return fuelleft; }