Mohan, Aman and Sohan together can complete a work in 18 days. If Mohan can work thrice as faster than Aman and Aman can work twice as faster than Sohan, then in how many days Sohan alone can complete the same work?

Let the amount of work completed by a person in one day be called that person’s work rate.

Assume Sohan’s one-day work rate is $$x$$ (fraction of the job finished per day).

Given: Aman works twice as fast as Sohan, so Aman’s rate is $$2x$$.
Given: Mohan works thrice as fast as Aman, so Mohan’s rate is $$3 \times 2x = 6x$$.

The combined one-day work rate of all three is therefore
$$x + 2x + 6x = 9x.$$

Together they finish the entire job in 18 days, so their combined rate equals $$\frac{1}{18}$$ job per day:

$$9x = \frac{1}{18}.$$

Solve for $$x$$:

$$x = \frac{1}{18 \times 9} = \frac{1}{162}.$$

Thus Sohan alone completes $$\frac{1}{162}$$ of the work each day, so he needs 162 days to finish the whole job.

Option B which is: 162 days