X can finish a work in 18 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 choices:  A) 5  B) 4  C) 6  D) 7  E) 8

Rationale: "work done by x in 1 day = 1 / 18 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 / 18 ) = 6 c"
Answer: C