A, B and C rent a pasture. If A puts 10 oxen for 7 months, B puts 12 oxen for 5 months and C puts 15 oxen for 3 months for grazing and the rent of the pasture is Rs. 210, then how much amount should C pay as his share of rent? Choose the correct choice from the following:
A) 54  B) 45  C) 25  D) 15  E) 55

Rationale: "a : b : c = 10 × 7 : 12 × 5 : 15 × 3 = 2 × 7 : 12 × 1 : 3 × 3 = 14 : 12 : 9 amount that c should pay = 210 × 9 / 35 = 6 × 9 = 54 answer is a"
Answer: A