12 men and 8 women can do a piece of work in 16 days. 13 men and 4 women can do it 18 days in how many days 3 men and 12 women complete the same work is 

$16(12M+8W)=18(13M+4W)$

$\Rightarrow 192M-234M=72W-128M$

$\Rightarrow 42M=56W$

$\Rightarrow 3M=4W$

$12M+8W=12M+2\left(3M\right)=12M+6M$

$=18M\to 16$ days

$3M+12W=3M+\left(4W\right)3$

$=3M+3\left(3M\right)$

$=3M+9M$

$=12M$

$18M-16Days$

$12M-?$

$=\frac{18}{12}\times 16=24$ days