The fuel cost per hour for running a train is proportional to the square of the speed generated in km/h. if the fuel cost is Rs.48/h at 16 km/h . It the fixed charges amount to Rs.1200/h
The most economical speed to run the train is:

Options

A. 18 km/h
B. 5 km/h
C. 80 km/h
D. 40 km/h

Answer

C