A granite rock ( = 2700 kg/m3, specific heat = 0.79 kJ/kg-K) with m = 5000 kg,

Question:

A granite rock (ρ = 2700 kg/m3, specific heat = 0.79 kJ/kg-K) with m = 5000 kg, heats up to T = 45oC during daytime due to solar heating. Assuming the surroundings to be at 20oC, determine
(a) the maximum amount of useful work (W) that could be extracted from the rock. What-if Scenario: What would the answer be if
(b) the rock temperature increased by 5oC or
(c) the ambient temperature decreased by 5 oC?