Answer:
y = 3 used games
x = 4 new games
Step-by-step explanation:
54x + 9y = 243
x + y = 7 then x = 7 - y
substitute for x:
54(7 - y) + 9y = 243
378 - 54y + 9y = 243
reduce:
378 - 45y = 243
subtract 243 from each side:
135 - 45y = 0
add 45y to each side:
45y = 135
divide both sides by 45:
y = 3
x = 7 - 3 = 4
check:
3+4 = 7
7 = 7
54(4) + 9(3) = 243
243 = 243