IBPS RRB Office Assistant Mains 6 Oct 2024 Shift 1 Paper

Given that A and B together can finish a task in 12.5 days, and B and C together can do it in 18.75 days, and also A and C together can do it in 15 days, how long would it take for A, B, C and D (with D having only 40% of C's efficiency) to complete the same task collectively?