A mixture of milk and water measures 60 litres. It contains 10% water. How much water should be added to it, so that the water may be 25%?

\[\begin{array}{*{20}{c}} {\,\,\,\,\,\,\,\,\,\,10\% }&{}&{100\% } \\ {}&{\,\,\,\,\,\,\,\,\,\,\,\,\,25\% }&{} \\ {\,\,\,\,\,\,\,\,\,\,75\% }&{}&{15\% } \\ {60 \leftarrow 5\,\,}&{\,\,\,\,\,\,\,\,\,\,\,:}&{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,1 \to 12{\text{ litres}}} \end{array}\]