It takes Avery 3 hours to build a brick wall while Tom can do it in 5 hours. If the two start working together and after an hour Avery leaves, how much time will it take Tom to complete the wall on his own?	Choose one:
A) 100
B) 110
C) 120
D) 130
E) 140

Rationale: "avery takes 3 hours tom takes 2 hours efficiency of avery is 1 / 3 units / hr efficiency of tom is 1 / 5 units / hr combined efficiency of tom and avery is 1 / 3 + 1 / 5 = 8 / 15 units / hr since they worked for 1 hour they completed 8 / 15 units of work and 7 / 15 units of work is left which is to be completed by tom ( since avery left ) so time taken by tom to complete the remaining work will be 7 / 15 / 1 / 5 hours = > 7 / 3 * 60 = 140 minutes . . . answer will be ( e )"
Answer: E