Working at a constant rate, P can finish a job in 3 hours. Q, also working at a constant rate, can finish the same job in 9 hours. If they work together for 2 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 options:  A) 20  B) 30  C) 40  D) 50  E) 60

Rationale: "each hour they complete 1 / 3 + 1 / 9 = 4 / 9 of the job . in 2 hours , they complete 2 ( 4 / 9 ) = 8 / 9 of the job . the time for p to finish is ( 1 / 9 ) / ( 1 / 3 ) = ( 1 / 3 ) hour = 20 minutes the answer is a ."
Answer: A