**Concept: The question tests on the ability to solve basic questions on Mensuration**

**Solution:**

12 inches = 1 foot

18 inches = 18/12 = 3/2 feet

Let the base of the rectangular box = a. Then the volume = a * a * h = 3/2a^2

3/2a^2 = 24

a^2 = 24 * 2/3 = 16

a = 4

Option A