These questions are usually hard. Be patient.
For 4b, I got 48. (bah i dont know if i'm doing it wrong)
"A (area of sheet metal) = x^2 + 4hx
But h = 32/(x^2)
Sub in to get: A = 128/(x^2) + x^2"
If you sub in, shouldn't you get: A = x^2 + 4(32/x^2)x = x^2 + 128/x ?