Answer :

Ok so the formula is SA = 2(l)(w) + 2(l)(h) + 2(w)(h). Plug the numbers in. SA = 2(3)(9) + 2(3)(13) + 2(9)(13). Multiply the numbers; 2·3·9=54. 2·13·3=78. 2·9·13=234. Now you have SA= 54 + 78 + 234. Add them together and SA= 366mm²
iGreen
SA = 2(wl+hl+hw)

SA = 2((3)(13) + (9)(13) + (9)(3))

Multiply:

SA = 2(39 + 117 + 27)

Add:

SA = 2(183)

Multiply:

SA = 366