Ajay can do a piece of work in 18 days and Divya can do the same work in 9 days. They started the work. After 3 days Sanjana joined them, who can complete alone the same whole work in 3 days. What is the total number of days in which they had completed the work?

In time and work problems, work = rate × time. Total work = LCM(18, 9, 3) = 18 units. Ajay's rate = 1 unit/day, Divya's rate = 2 units/day, Sanjana's rate = 6 units/day. First 3 days: Ajay + Divya = 3 units/day. Work done = 3 × 3 = 9 units. Remaining = 18 - 9 = 9 units. With Sanjana: combined rate = 1 + 2 + 6 = 9 units/day. Time = 9/9 = 1 day. Total = 3 + 1 = 4 days. Option B is correct.