A granite sphere having a diameter of 15 cm and initially at a uniform temperature of 120C is suddenly exposed to a convection environment with

A granite sphere having a diameter of 15 cm and initially at a uniform temperature of 120ºC is suddenly exposed to a convection environment with h = 350 W/m2 · ºC and T = 30ºC. Calculate the temperature at a radius of 4.5 cm after 21 min and the energy removed from the sphere in this time. Take the properties of granite as k = 3.2 W/m · ºC and α = 13 × 10−7 m2/s.