18...let x is the number pair of shoes selling
a. 8x +200
b. 12x + 160
c. 8x + 200 = 12x + 160 solve for x
8x + 200 = 12x + 160
8x - 12x = 160 - 200
-4x = -40
x = -40/-4
x = 10
d. the number (x=10) found in "c" means Mike sells 10 pair of shoes in a week