Annu and Bhanu undertook a piece of work for Rs 600. Annu alone can do it in 6 days while Bhanu alone can do it in 8 days. With the help of Charu, they can finish it in 3 days, Find the share of Charu?

Annu's 1-day work = 1/6, Bhanu's 1-day work = 1/8. Together they do 1/6 + 1/8 = 7/24 per day. In 3 days with Charu, they complete the work, so combined 1-day work = 1/3. Charu's 1-day work = 1/3 - 7/24 = 1/24. Charu's 3-day work = 3/24 = 1/8. Charu's share = (1/8) * 600 = Rs. 75. Option D is correct. Option A (80) would be 1/7.5, B (85) is 1/7.06, C (70) is 1/8.57 - none match the calculation.