X can finish a work in 21 days. Y can finish the same work in 15 days. Y worked for 5 days and left the job. how many days does X alone need to finish the remaining work?
Select the correct option:  A) 12  B) 13  C) 16  D) 14  E) 18
Work done by X in 1 day = 1/21   Work done by Y in 1 day = 1/15   Work done by Y in 5 days = 5/15 = 1/3   Remaining work = 1 – 1/3 = 2/3   Number of days in which X can finish the remaining work = (2/3) / (1/21)= 
<gadget id="calculator">(2/3) / (1/21)</gadget>
<output>14</output>
14   14
<result>D</result>
X can finish a work in 21 days. Y can finish the same work in 15 days. Y worked for 5 days and left the job. how many days does X alone need to finish the remaining work?