An engine does 15.0 kj of work while exhausting 37.0 kj to the cold reservoir. what is the efficiency of the engine?

28.8 %

Explanation:

The efficiency of an engine is given by:

where

W is the useful work done

is the heat in input

For this machine, we have

W = 15.0 kJ is the work done

is the heat exchausted to the cold reservoir, so the total amount of heat in input is

And so the efficiency is

which corresponds to 28.8 %.