A and B together can complete a piece of work in 35 days while A alone can complete the same work in 60 days. B alone will be able to complete the same work in :

42 days 72 days 84 days 96 days

84 days

The above chart was obtained after following the details of the question: Efficiency of A+B = 12 Efficiency of A = 7 Efficiency of B = 12-7 = 5 Days required by B alone to complete the work = \(\frac{420 }{5 }\) = 84 days