Answer:
684 sq.ft
Step-by-step explanation:
(1) The base area of the pyramid is 18x20=360 sq.ft
(2) The Triangles of the pyramid:
1. There are two kinds of the triangles.
2. Smaller one: 18x8/2 (base times height divide 2)=72 sq.ft
3. Bigger one: 20x9/2=90 sq.ft
4. There are two of them so 72+72+90+90=324 sq.ft
And so 360+324=684 sq.ft.