determine the total amount of heat removed from each bearing during this time

Question

Steel ball bearings (K = 50 W/m-K, a = 1.3 ´ 10^–5 m²/s) having a diameter of 40 mm are heated to a temperature of 650 ⁰C and then quenched in a tank of oil at 55 ⁰C. If the heat transfer coefficient between the ball bearings and the oil is 300 W/m²-K, determine -

1. the duration of tie the bearings must remain in oil to reach a temperature of 200 ⁰C;
2. the total amount of heat removed from  each bearing during this time;
3. the instantaneous heat transfer rate from the bearings when they are first immersed in oil and when they reach 200 ⁰C.