Akash is thrice as good a workman as Baldev and therefore is able to finish a job in 40 days less than Baldev. Working together, they can do it in

Ratio of times taken by Akash and Baldev = 1 : 3

The time difference is (3 - 1) 2 days while Baldev take 3 days and Akash takes 1 day.

If difference of time is 2 days, Baldev takes 3 days.

If difference of time is 40 days, Baldev takes = $$\frac{3}{2} \times 40 = 60$$ days

So, Akash takes 20 days

Akash's 1 day's work = $$\frac{1}{20}$$

Baldev's 1 day's work = $$\frac{1}{60}$$

(Akash + Baldev)'s 1 day's work together = $$\frac{1}{20} + \frac{1}{60} = \frac{4}{60} = \frac{1}{15}$$

$$\therefore$$ Akash and Baldev together can do the work in = 15 days

=> Ans - (D)