In the heat treating process in a sheet-metal manufacturing plant, brass plates are annealed by first heating them in an industrial furnace oven the inside of which is maintained at a constant uniform temperature of 550°C. If the surface of the brass plate, which has a thickness of 2.5 cm, is initially at a uniform temperature of 25°C, determine the time required for heating the plate surface to 300°C after the plate has been placed inside the oven. Consider that heat transfer from the oven gases to the plate is by convection and that h̅_c = 135 W/m² K.