Math problem-It took Party A and Party B 8 days to finish a piece of work, but it took Party C 6 days to finish it. It took Party C 12 days to complete it. How many days will it take Party A and Party D to complete? The first method: first calculate the work efficiency of four people:1/8+112 = 5/24, and then subtract the efficacy of b and c from the efficacy of four people: 5/24- 1/6= 1/24. The second method: first add up all the efficacy:1/8+1/6+112 = 3/8. This is equivalent to calculating the efficacy of two ethylene propylene and one butyl, so we should use the previous method to calculate all the efficacy, MINUS the efficacy of two ethylene propylene: 3/8.