Explanation:
we need to see how many cubes fit into every dimension.
we can fit 4 cubes along the 1 in width. as 4×1/4 = 1 in.
we can fit 15 cubes along the 3 3/4 in length :
3 3/4 = 12/4 + 3/4 = 15/4
15/4 / 1/4 = 15/4 × 4/1 = 4×15 / 4×1 = 15
we can put 6 cubes on top of each other fit the height of 1 1/2 in
1 1/2 = 2/2 + 1/2 = 3/2 = 6/4
6/4 / 1/4 = ... = 6 (as above - simply 1/4 fits 6 times into 6/4).
so, we have
4 × 15 × 6 = 360
we need 360 cubes to fill the box.