Answer:
Shirt = $7
Sweatshirt = $12
Explanation:
Let T represent shirts and S to represent sweatshirts
you bought 3T + 4S = 69
your friend bought 6T + 2S = 66 multiply second equation by -2
-2 x 6T + 2S = 66
-12T - 4S = -132 now find the sum of this and first equation
3T + 4S -12T - 4S = 69 - 132 add like terms
-9T = -63 divide both sides by -9
T = 7 this is the cost of one shirt to find the cost of a sweatshirt we replace the T in any equation with 7
3T + 4S = 69
3*7 + 4S = 69
21 + 4S = 69 subtract 21 from both sides
4S = 48 divide both sides by 4
S = 12