If you want to find the surface area of something and it doesn't have a formula, just look at the area of each side individually and add them up!
The area of a triangle is equal to bh/2 = 16*6/2 = 48 in²
The area of the other triangle would be the same = 48 in²
The lateral side that's 10 by 9 inches = 10 * 9 = 90 in²
The other lateral side that's 10 by 9 is also = 90 in²
The lateral side that's 16 by 9 inches = 16 * 9 = 144 in²
144 + 90 + 90 + 48 + 48 = 420 in²
