3 men or 5 women can do a work in 12 days. How long will 6 men and 5 women take to finish the work?

Let assume the amount of work be 180 units

It is given that 3 men can do 180 units of work in = 12 days

then 1 men's 1 day work = 5 units

6 men's 1 day work = 6 x 5 = 30 units

Now it is also given that 5 women do the same amount of work of 180 units in = 12 days

so, 5 women's 1 day work = 15 units

Now, (6 men + 5 women)'s 1 day work = (30+15) = 45 units

So, number of days required by (6 men + 5 women) to complete 180 units of work = $$\frac{180}{45}$$ = 4 days