Working at a constant rate, P can finish a job in 4 hours. Q, also working at a constant rate, can finish the same job in 15 hours. If they work together for 3 hours, how many more minutes will it take P to finish the job, working alone at his constant rate?	Choose the correct choice from the following
A) 5  B) 8  C) 10  D) 12  E) 15

Rationale: "each hour they complete 1 / 4 + 1 / 15 = 19 / 60 of the job . in 3 hours , they complete 3 ( 19 / 60 ) = 19 / 20 of the job . the time for p to finish is ( 1 / 20 ) / ( 1 / 4 ) = ( 1 / 5 ) hour = 12 minutes the answer is d ."
Answer: D