Explanation:
w(idth) = 2.5 inches for both boxes
h(eight) = 10 inches for both boxes
l(ength)l(arge) = 8 inches
l(ength)s(mall) = 75% of ll (=> of 8 inches)
=> ls = 8 × 75/100 = 2 × 75/25 = 2 × 3 = 6 inches
vl (volume large) = 8 × 2.5 × 10 = 200 inches³
vs (volume small) = 6 × 2.5 × 10 = 150 inches³
the difference of these two volumes is 50 inches³
the units to be used is cubic inches (inches³). we are talking about volumes. not lengths (inches), not areas (inches²).
the reason - for a volume we need to multiply 3 lengths (measured in simple inches). so, inch multiplied by inch is inch². this multiplied by inch again is then inch³.