First, we need to convert 4 ft into inches.
1 ft is equivalent to 12 in, then 4 ft is equivalent to 4x12 = 48 in.
To find how many cubes with side lengths of 3 inches fit in a larger cube with side lengths of 48 inches, we need to divide the larger length by the shorter length, as follows: 48/3 = 16. That is, she can fit 16 Kleenex boxes into the larger box.