X can finish a work in 21 days. Y can finish the same work in 15 days. Yworked for 10 days and left the job. how many days does X alone need to finish the remaining work? Choose the correct choice from the following
A) 3	B) 5	C) 7	D) 8	E) 9
Work done by X in 1 day = 1/21   Work done by Y in 1 day = 1/15   Work done by Y in 10 days = 10/15 = 2/3   Remaining work = 1 – 2/3 = 1/3   Number of days in which X can finish the remaining work = (1/3) / (1/21)= 
<gadget id="calculator">(1/3) / (1/21)</gadget>
<output>7</output>
7   7
<result>C</result>
X can finish a work in 21 days. Y can finish the same work in 15 days. Yworked for 10 days and left the job. how many days does X alone need to finish the remaining work?