An oil bath maintained at 40°C with a convective coefficient 500 W/m2·K is used to quench stainless steel spherical ball bearings ( 25 W/m·K, 4.85 x 10-6 m2/s) in order to harden them. Consider a ball bearing of uniform temperature 850°C and a diameter of 40 mm. How long, in seconds, will it take for the surface temperature of the sphere to reach 100°C? What is the corresponding center temperature, in °C?