Question

The base of a rectangluar prism is 5 meters by 3 meters. the height of the prism is 7 meters. the total surface area, except for one face, is 121 square meters. What are the dimesions of the missing face?

Answer 1

Total SA = top + bottom + 2 (short side) + 2 (long side)
top = bottom = 5×3 = 15
short side = 7×3 = 21
long side = 7×5 = 35
SA = 2 (15) + 2 (21) + 2 (35) = 30+42+70 = 142
So 142 - 121 = 21, so the missing face is a short side of 7×3