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 apple2 = new Apple();
        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;