x = small boxes and y = large boxes
x + y = 17.....x = 17 - y
3x + 14y = 183
3(17 - y) + 14y = 183
51 - 3y + 14y = 183
-3y + 14y = 183 - 51
11y = 132
y = 132/11
y = 12 <=== large boxes (y) cost $ 12
x + y = 17
x + 12 = 17
x = 17 - 12
x = 5 <=== small boxes (x) cost $ 5
