Question 399225
 
The formula for the volume of a square based pyramid is: (1/3)(b^2)(h) OR (b^2)(h)/3 

You square root the base as its a square and there both the same

So it will be:= 1/3 x 3.5^2 x 4 
              = 16.3 ft cubic

Let me know if that helps, or if you want me to go over it?