6*7=42 => less than 45
6*8=48 => more than 45
6*9=54 => more than 45
Since they asked for all the shirts, then 7 boxes is an insufficient amnt.
And since both 8 and 9 boxes can hold all 45 shirts and more then, between 8 and 9,which is less?
The obvious answer is 8 making 8 your answer!!