x = # of posters, y = total cost
y = 2x + 250
y = 1000
1000 = 2x + 250
1000 - 250 = 2x
750 = 2x
750/2 = x
375 = x....so 375 posters can be printed
==========================
y = total cost, x = # of miles
y = 3x + 3
y = 117
117 = 3x + 3
117 - 3 = 3x
114 = 3x
114/3 = x
38 = x.....so the car was towed 38 miles
