The fuel charges for running a train are proportional to the square of the speed generated in \(...

The fuel charges for running a train are proportional to the square of the speed generated in \( \mathrm{km} / \mathrm{h} \), and the cost is \( ₹ 48 \) at \( 16 \mathrm{~km} / \mathrm{h} \). If the fixed charges amount to ₹ \( 300 / \mathrm{h} \), the most economical speed is
(A) \( 60 \mathrm{~km} / \mathrm{h} \)
(B) \( 40 \mathrm{~km} / \mathrm{h} \)
(C) \( 48 \mathrm{~km} / \mathrm{h} \)
(D) \( 36 \mathrm{~km} / \mathrm{h} \)