A cistern is filled by three faucets with uniform flow. The first two faucets operating simultaneously fill the cistern in the same during which the cistern is filled by the third faucet alone. The second faucet fills the cistern 5 hours faster than the first faucet and 4 hours slower than the third faucet. The time required by the first faucet is? A) 6 hrs B) 10 hrs C) 15 hrs D) 30 hrs