19. A furnace manufacturer wants to know how much of the metal surface area is giving off heat in this design. The metal box is cube-shaped (all sides equal) with sides measuring 40 in. The circular metal vent is 30 in tall with a diameter of 8 in. Calculate the surface area giving off heat, excluding the cube's base and the bottom and top of the vent tube. (Hint: You must also subtract the area of the circle where the vent connects to the cube.) (5 marks)