If 10 litres of an oil of Rs.54 per litres be mixed with 5 litres of another oil of Rs.66 per litre then what is the rate of mixed oil per litre?  Select the correct option:
A) rs . 49.17 B) rs . 58 C) rs . 54.17 D) rs . 55.33 E) none of the above

Rationale: "54 * 10 = 540 66 * 5 = 330 870 / 15 = 58 answer : b"
Answer: B