A ship, 40 km from the shore, springs a leak which admits 3 3/4 tonnes of water in 15 min. 60 tonnes would suffice to sink her, but the ship’s pumps can throw out 12 tonnes of water in one hour. Find the average rate of sailing, so that it may reach the shore just as it begins to sink.

A

$$1\frac{1}{2}$$ km/h

B

$$2\frac{1}{2}$$ km/h

C

$$3\frac{1}{2}$$ km/h

D

2 km/h