Make a system of equation
Let L be large pictures
Let S be small pictures
You know they add to 16 pictures
You know each cost
(L + S = 16) * 25
25L + 20S = 350
25L + 25S = 400
Subtract (elimination method)
-5S = -50, S = 10
L + 10 = 16, L = 6
Solution: 10 small pictures
6 large pictures
