Asquare pyramid base perimeter of 12 ft and a height of 9 ft, what is the volume?

Volume of pyramid is V = (lwh) / 3. 
3
It says it's a square pyramid, so all its sides of its base are the same. 
Permiter is 12, so each sides is 3 (12 divided by 3). 

Now you know that the length and width are both 3.

Plug it all in the formula. 
V = (3*3*9) / 3
V = 81/3
V = 27

The volume is 27ft^3, 27 cubic feet