Hi there!
First, we need to determine the volume.
1/2 × 2 × 7/2 = 7/2 in cubed
3.5 cubes with sidelengths of 1in can fit in, since both units are three dimensional and 7/2 ÷ 1 = 3.5
7 cubes with sidelengths of 1/2 can fit because 7/2 ÷ 1/2 = 7
Hope this helps!