12 x 12 x 6 mailing boxes

A fun math problem!

Let's break it down step by step:

1. 12 x 12 = 144 (area of the base of the box)
2. 144 x 6 = 864 (volume of the box)

So, you would need 864 cubic inches of space to fit 12 x 12 x 6 mailing boxes.