The speed of a metro engine is 42 km/hr when no compartment is attached and reduction of speed is directly proportional of the square root of the number of compartments attached. If the speed of the train carried by this engine is 24 km/hr when 9 compartments are attached, the maximum number of compartments that can be carried by the engine is -

• A. 48
• B. 47
• C. 49
• D. None of these