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) 6 days
B) 7 days
C) 8 days
D) 5 days
E) 2 days
4/10 + 9/x = 1 =&gt; x = 15   1/10 + 1/15 = 1/6 =&gt; 6 days   \6 daysnswer:6 days
<result>A</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?