If 12 men or 15 women or 18 boys can do a piece of work in 15 days of 8 hours each, find how many men assisted by 5 women and 6 boys will finish the same work in 16 days of 9 hours each.

Given, 

$12$ men$=15$women $=18$ boys

$\therefore$$1$ Man $= 1.5$boys, $1$ woman$= 6/5$ boys.

Now,

$\mathrm{SW}+ 6\mathrm{B} = 12\mathrm{B}$

Required answer is calculated as follows :

Total no. of boys reqd

$=18\times \left[\right(15/16)\times (8/9\left)\right]$

$=15$ boys

The number of boys already present$= 12.$

Hence, $3$ boys more required.

But $3$ boys $=2$ men. 

So, $2$ men are required.