Check the picture below.
so the pyramid is really just 4 triangular faces with a base of 8 and a height of 5 and an 8x8 square at the bottom.
[tex]\stackrel{\textit{\large Areas}}{\stackrel{base}{(8\cdot 8)}~~ +~~\stackrel{4~triangles}{4\left[\cfrac{1}{2}(8)(5) \right]}}\implies64+20\implies 84[/tex]
