A square based pyramid has a surface area of 256.7 and a base length of 7.2. what is the slant height of the pyramid

If we consider that the pyramid has a solid "bottom"...the area of this "bottom" =  7.2² = 51.84 sq units

And subtracting this from 256.7 gives the total area of the sides = 204.86 sq units. And the area of each side is 1/4 of this = 51.215 sq units

And since each side is a triangle with a base of 7.2, we have

51.215 = (1/2)*7.2* h    

51.215 = 3.6 * h      divide both sides by 3.6

h = about 14.23 units = the slant height