A and B can together finish a work in 40days. They worked together for 10days and then B left. After another 15days, A finished the remaining work. In how many days A alone can finish the job?
Choose the correct choice from the following.
A) 10 B) 25 C) 60 D) 30 E) 20

Rationale: "a + b 10 days work = 10 * 1 / 40 = 1 / 4 remaining work = 1 - 1 / 4 = 3 / 4 3 / 4 work is done by a in 15 days whole work will be done by a in 15 * 4 / 3 = 20 days answer is e"
Answer: E