Ravi can do a piece of work in 15 days while Prakash can do it in 6 days. In how many days will they finish it together?
Choose one:	A) 5 7/9 days	B) 6 7/9 days	C) 5 1/9 days	D) 5 7/2 days	E) 4 2/7 days
1/15 + 1/6 = 7/30   30/7 = 4 2/7 days   ANSW4 2/7 daysR:4 2/7 days
<result>E</result>
Ravi can do a piece of work in 15 days while Prakash can do it in 6 days. In how many days will they finish it together?