the base of the pyramid is a square, meaning all of its sides are 24 inches.
the slant-height, or the altitude of the triangular face, is 20 inches.
now, we can simply get the area of the squarish base, and all four triangular faces, since each one has a base of 24 and a height of 20, sum them up, and that's the area of the pyramid.
[tex]\bf \stackrel{\textit{area of the base}}{(24\cdot 24)}~~+~~\stackrel{\textit{area of the four triangles}}{4\left[\cfrac{1}{2}(24)(20) \right]}\implies 576~~+~~960\implies 1536[/tex]
