A can do a work in 12 days. When he had worked for 3 days, B joined him. If they complete the work in 3 more days, in how many days can B alone finish the work?
A. 6 days
work done by A for 3 days = 3/12=1/4 Remaining work = 1 - 1/4 = 3/4
work done by (A+B) for 1 day=(3/4)*(1/3)=1/4
work done by B for 1 day=(1/4)-(1/12)=2/12=1/6.
B alone will complete the work in 6 days