Wally Whacko claims to have invented a heat engine that will revolutionize industry. It runs between a

Question:

Wally Whacko claims to have invented a heat engine that will revolutionize industry. It runs between a hot source at 300°C and a cold sink at 25°C. He claims that his engine is 92% efficient.
(a) What error did he make in his choice of temperature scales?
(b) What is the actual maximum efficiency of his engine?