1 table equals 3 chairs, and 4 tables equals 3*4= 12 chairs. Each chair: 252/2 1= 12 yuan. Each table: 12*3=36.
It takes 10 day for Party A to do it, and 15 day for Party B to finish it, which means that if Party A does 5 days more, Party B will do 7.5 days less, which means that it takes 7.5 days for Party A to do it, and 7.5+22.5=30 days for Party B to do it alone, then Party A will get 20 days.