Two equal glasses are respectively $\frac{1}{3}$ and $\frac{1}{4}$ full of milk. They are, then filled up with water and the contents are mixed in a tumbler. Find the ratio of milk and water in the tumbler.

A contractor took a contract for building $12$ kilometer road in $15$ days and employed $100$ labors on the work. After $9$ days, he found that only $5$ kilometer road had been constructed. How many more labors should be employed to ensure that the work may be completed within the given time?