24.51 just add all the prices together and subtract from 30!
What points are A and C? I can see that point B is (-5,3) and point D is (2,1) but what is point A and point C?
Anything withdrawn you subtract. Then, you know the total and you know what you had. Subtract total from what you had and you will see the change.
1735.97-100=1635.97
1668.71-1635.97=32.74