I'm a totally new to processing, like 2 or 3 days in, and I cam upon the first thing i really am having trouble trying tp troubleshoot. there is an error message when attempting to run the app (schoolApp)

schoolApp is:

2. 
   
3. 
   
4. import ddf.minim.*;
5. 
   
6. ImageButton play, next, last;
7. 
   
8. // Images for buttons
9. PImage playBase, playOver, playDown, nextBase, nextOver, nextDown, lastBase, lastOver, lastDown;
10. 
    
11. // Background colors
12. int r, g, b = 0;
13. 
    
14. // Position of and size of image buttons
15. int x, y, w, h, xn, xp, xl;
16. 
    
17. // Custom External class's
18. 
    
19. Button button;
20. 
    
21. 
    
22. 
    
23. void setup() {
24.   size(640, 480);
25.   background(r, g, b);
26.   playBase = loadImage("playBase.png");
27.   playOver = loadImage("playOver.png");
28.   playDown = loadImage("playDown.png");
29.   nextBase = loadImage("nextBase.png");
30.   nextOver = loadImage("nextOver.png");
31.   nextDown = loadImage("nextDown.png");
32.   lastBase = loadImage("lastBase.png");
33.   lastOver = loadImage("lastOver.png");
34.   lastDown = loadImage("lastDown.png");
35.   x = width;
36.   y = height*9/12;
37.   w = 72;
38.   h = 72;
39.   xn = x*2/12;
40.   xp = x*5/12;
41.   xl = x*8/12;
42. 
    
43.   next = new ImageButton(x, y, w, h, nextBase, nextOver, nextDown);
44.   play = new ImageButton(x, y, w, h, playBase, playOver, playDown);
45.   last = new ImageButton(x, y, w, h, lastBase, lastOver, lastDown);
46. }
47. 
    
48. void draw() {
49.   next.update();
50.   play.update();
51.   last.update();
52.   next.display();
53.   play.display();
54.   last.display();
55. }
56. 
    

imageButton is

2. class ImageButton extends Button {
3. 
   
4.   PImage Base;
5.   PImage Over;
6.   PImage Down;
7.   PImage currentimage;
8. 
   
9.   ImageButtons(int ix, int iy, int iw, int ih, Pimage iBase, PImage iOver, Pimage iDown) {
10.     x = ix;
11.     y = iy;
12.     w = iw;
13.     h = ih;
14.     Base = iBase;
15.     Over = iOver;
16.     Down = iDown;
17.     currentimage = base;
18.   }
19. 
    
20.   void update() {
21.     over();
22.     pressed();
23.     if (pressed) {
24.       currentimage = Down;
25.     } 
26.     else if (over) {
27.       currentimage = Over;
28.     } 
29.     else {
30.       currentimage = Base;
31.     }
32.   }
33. 
    
34.   void over() 
35.   {
36.     if ( overRect(x, y, w, h) ) {
37.       over = true;
38.     } 
39.     else {
40.       over = false;
41.     }
42.   }
43. 
    
44.   void display() 
45.   {
46.     image(currentimage, x, y);
47.   }
48. }

if I could get some help that would be greatly appreciated

i will post the code on github if it helps to get everything I have.