A and B can finish a piece of work in 20 days .B and C in 30 days and C and A in 40 days. In how many days will A alone finish the job?

A. 48
B. 34(2/7)
C. 44
D. 45

(1/A)+(1/B) = (1/20) (1/B)+(1/C) = (1/30) (1/A)+(1/C) = (1/40) Solving the three equations,
A=48