The base of the pyramid is the side length squared
Base Area = (side length)(side length)
= (8.2)(8.2)
= 67.24
The slant length and side length is used to calculate the area of one slated face of the pyramid. Using the formula for a trangle (bh/2) we can find the area of one face
Face= bh/2
= 8.2(15.9)/2
= 130.38/2
= 65.19
As there are 4 faces, and one base the total area is the sum of 4 faces and the base area
A= 4F+BA
= 4(65.19) + 67.24
= 260.76 + 67.24
= 328 in²