It takes 125 identical wooden cubes to fill a cubical box. How many of these cubes does it take to cover the bottom of the box?

Question

Could someone explain this one to me?

Answer 1

125 is a perfect cube, namely 5^3
so the box is 5 by 5 by 5
and the area of the bottom would be 25,
so it would take 25 of the cubes to fill the bottom layer.