I figured it out after a while, but can someone explain why in this example "Apple.applePrice" works and "this.applePrice" doesn't? I'm sure it has to do with the difference in static and non-static but I don't understand it. 
public class Solution {
    public static void main(String[] args) {
        Apple apple = new Apple();
        apple.addPrice(50);
        Apple apple2 = new Apple();
        apple2.addPrice(100);
        System.out.println("The cost of apples is " + Apple.applePrice);
    }

    public static class Apple {
        public static int applePrice = 0;

        public static void addPrice(int applePrice) {
            Apple.applePrice += applePrice;
        }
    }
}