A man can do a piece of work in 6days, but with the help of his son, he can finish it in 3days. In what time can the son do it alone? Choose the correct choice from the following:
A) 5
B) 5 1/2
C) 7 1/2
D) 6
E) 9 1/2
Son's 1day work = 1/3 - 1/6 = 1/6   Son alone can do the work in 6 days = 6 days   Answer is 6
<result>D</result>
A man can do a piece of work in 6days, but with the help of his son, he can finish it in 3days. In what time can the son do it alone?