Description for Correct answer:
Let the required earnings be Rs.x.

More persons, More earnings (Direct proportion)

Less hours per day, Less earnings (Direct proportion)

Persons 36 : 30

:: 33600 : x

Hours per day 8 : 9

Therefore, \( \Large \left(12 \times 16 \times x\right)=\left(18 \times 12 \times 33600\right) \)

Therefore, \( \Large x = \frac{18 \times 12 \times 33600}{12 \times 16} = 18 \times 2100 \)

= Rs.37800.