Task: Question Answering
Input (English): Problem: a man can do a piece of work in 5 days, but with the help of his son, he can finish it in 4 days. in what time can the son do it alone ?
Options: a. 5, b. 5 1 / 2, c. 7 1 / 2, d. 6, e. 20
Output (English): e