3 men complete work in 43 days
so one man does 1/(3(43))th part of work daily
and one women does 1/(4(43))th path of work dail
so 7 men and 5 women will do
 \frac{7}{3(43)}+ \frac{5}{4(43)}= \frac{1}{43}( \frac{28+15}{12} )= \frac{1}{12}
so they do 1/12th part of work daily
so they will complete the work in 12 days
4 4 4
12 days to construct .. 
1 5 1