To find surface area we can do 2(l)(w) + 2(l)(h) + 2(h)(w). l = length; w = width; h = height.
Next
Plug in 3 for length, 9 for height, and 13 for width. ( or however you’d like for width length height but only one number can be represented by h, l, and w.)
Then we add all the numbers
2(3)(13)+ 2(3)(9) + 2(9)(13) = SA (surface area)
78 + 54 + 234 = 366 in^2 or 366 sq. inches
