FREE HINTS about VOLUME puzzles:

1) Volume is the amount of space an object takes up.

2) mm < cm < inches < feet

3) Doubling volume means TWICE AS MANY cubes.

4) Volume is 3-dimensional (length x width x height).  Area is 2-dimensional (length x width). Lines are 1-dimensional (length only).

5) Units for AREA is squared and VOLUME is cubed, but LENGTH is just units.