Answer
$12x+15y = 120$
Thee combinations: no shirts and 8 sweatshirts, 10 shirts and no sweatshirts, 5 shirts and 4 sweatshirts
Work Step by Step
12 per shirt, 15 per sweatshirt, 120 to spend
$12x+15y = 120$
Let x = 0:
$12*0 + 15y = 120$
$15y = 120$
$15y/15 = 120/15$
$y = 8$
Let y = 0:
$12x + 15*0 = 120$
$12x = 120$
$12x/12 = 120/12$
$x = 10$
Let x = 5:
$12*5 + 15y = 120$
$60 + 15y = 120$
$60 + 15y -60 = 120-60$
$15y = 60$
$15y/15 = 60/15$
$y =4 $
