A horizontal copper plate 10 cm thick is initially uniform in temperature at 250C. The bottom surface

Question:

A horizontal copper plate 10 cm thick is initially uniform in temperature at 250ºC. The bottom surface of the plate is insulated. The top surface is suddenly exposed to a fluid stream at 80ºC. After 6 min the surface temperature has dropped to 150ºC. Calculate the convection heat-transfer coefficient that causes this drop.