Well let's see.... 6/3=2. To check your work simply measure 2x3 and you get 6.
The reason this is: Due to Aarons poster being 6 square feet, the length is 3 and the only other least common multiple for 6 besides 1 and itself and 3 would be 2, leaving that to be your final answer.
BTW: This is a formula, which can work for either Area or Volume.