(1) Take this project as 1, assuming that it takes X days for B to finish it alone. Then a completes 1/40 every day, and b completes 1/x every day. (30/x)+(1/40+1/x) * 20 =1,and the value of x can be obtained by solving this equation. x= 100 .

(2)x/40+y/ 100= 1, that is, 5x+2y=200. Because x and y are integers, and x