A can do a piece of work in 10 days. He works at it for 4 days and then B finishes it in 9 days. In how many days can A and B together finish the work?
Select.
A) 4 days	B) 2 days	C) 6 days	D) 8 days	E) 9 days
6 days   6 days   4/10 + 9/x = 1 =&gt; x = 15   1/10 + 1/15 = 1/6 =&gt; 6 days
<result>C</result>
A can do a piece of work in 10 days. He works at it for 4 days and then B finishes it in 9 days. In how many days can A and B together finish the work?