There is a mistake 9,12,13 is not a right triangle. but 9,12,15 is. IF you use this triangle instead, then the area of the 13,14,15 triangle is the sum of the area of the other two triangles.
1/20 is the fraction that you'll have left
60 t-shirts and 44 shorts
You can get this by setting up a system of equations:
x + y = 104
25x + 15y = 2160
Alternate Interior angles