13. Five marks exercise problems VIII

\(P\) alone can do $\frac{1}{2}$ of a work in \(6\) days and \(Q\) alone can do $\frac{2}{3}$ of the same work in \(4\) days. In how many days will they finish $\frac{3}{4}$ of the work, working together?

 

Number of days taken \(=\)  days