A heat engine is $20$% efficient. If the engine does $500J$ of work every second, how much heat does the engine exhaust every second?

The correct option is B $2000J$
Efficiency in percentage is defined as:

$\eta =\frac{\text{Work Done}}{\text{Heat energy supplied}}\times 100$

$20=\frac{500}{E_{in}}\times 100$

$E_{in}=2500J$

Heat energy exhausted is the difference of the heat energy supplied and effective work done. Hence, heat exhausted is given by:

$H=2500-500=2000J$