Question

Help, I still cannot wrap my head around this

Answer 1

9 inches.

Explanation:

Fun question! The length of a space diagonal for a cube is
`√(3*sidelength^2)`

Thus, the first cube has a side diagonal of
`√(3)`

The next cube would have a side diagonal of 3

The third cube would have a side diagonal of
`3√(3)`

And the fourth cube would have a side diagonal of 9.

Since the fifth cube has a side length equal to the side diagonal of the fourth cube, it should be 9 inches.