How many boxes that is 5" * 4" * 3" could be placed inside a big box of 40" * 32" * 24" ??

Compare each side of the small box:

5" * 4" * 3"
with the big box
40" * 32" * 24"

There are 40/5=8 rows times 32/4=8 rows times 24*3=8 rows.

So how many small boxes can the big box fit?