Explain about the Heat Extraction?

a) A body of mass M has a temperature-independent precise heat C. If the body is heated reversibly from a temperature T_i to a temperature T_f what is the change in its entropy?

b) Two such bodies are primarily at temperatures of 100 K and 400 K. A reversible engine is used to take out heat with the hotter body as a source and the cooler body as a sink. What is the maximum quantity of heat that can be extracted in units of MC?

c) The specific heat of water is C= 402j/g k  and its density is 1g/cm³ Calculate the maximum useful work  that can be extracted, using as a source 10³ m³ of water at  100°C and a lake of temperature 10°C as a sink.