answer: 974 squared inches
to find surface you do as such here:
length x height x 2 [two because you have two of each side for this certain shape] (462)
width x height x 2 (336)
length x width x 2 (176)
then once you have all of them, you add them together and have your surface area! i’ll show how i solved the height x length for you :)
21 x 11 x2
231 x 2 = 462
hope this made sense!