On a hot summer day a concrete driveway may reach a temperature of 50C. Suppose that a

On a hot summer day a concrete driveway may reach a temperature of 50ºC. Suppose that a stream of water is directed on the driveway so that the surface temperature is suddenly lowered to 10ºC. How long will it take to cool the concrete to 25ºC at a depth of 5 cm from the surface?