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 18 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? Options.
A) 32  B) 36  C) 40  D) 44  E) 48

Rationale: "each hour they complete 1 / 3 + 1 / 18 = 7 / 18 of the job . in 2 hours , they complete 2 ( 7 / 18 ) = 7 / 9 of the job . the time for p to finish is ( 2 / 9 ) / ( 1 / 3 ) = ( 2 / 3 ) hour = 40 minutes the answer is c ."
Answer: C