A can finish a price of work in 40 days. He worked alone for 15 days and then B joined him. Together they could finish the remaining work in 15 days, in how many days B alone can finish the same work?

A's 1-day work = 1/40. In 15 days, A completes 15/40 = 3/8 of work. Remaining work = 1 - 3/8 = 5/8. A and B together finish this in 15 days, so (1/40 + 1/B) × 15 = 5/8, giving (1/40 + 1/B) = 5/120 = 1/24. So 1/B = 1/24 - 1/40 = (5 - 3)/120 = 2/120 = 1/60. Therefore B alone can finish the work in 60 days. Option C is correct.