Power = Work / time
The work given here is 83J and the time it took to do 83J of work was 3s
So..
Power = 83J / 3s
Power = 27.67 W or 27.7 W

Actually Welcome to the Concept of the Methods of Separation.
Evaporation and Decantation are the process which can be easily used to remove the Soluble Impurities.
When a red giant has insufficient mass it pretty much sheds its outer layer to leave the center core know as the white dwarf
law of conservation of energy
aka the first law of thermodynamics