Next time, Shay, please include the instructions. I'm assuming that our job here is to determine the largest # of boxes of darts that can be purchased.
Shirt cost + x(box of darts cost) = Initial amount
$56 + x($6/box) = $80
Then 56 + 6x = 80, or 6x= 24, or x = 4. He can buy 4 boxes of darts.