**Answer**: (D) 7200 litres

**Explanation**: The capacity of tank = x litre (suppose)

Quantity of water emptied by the leak = (x/10) litres

Quantity of water admitted to the tank = (4 * 60) = 240 litre/hour

According to the question, (x/10) -(x/15) = 240

Therefore, x = 7200 litres