From the top of a building $20 \mathrm{m}$ high, the angle of elevation of the top of a monument is $45°$ and the angle of depression of its foot is $15°$. Find the height of the monument.

In the adjoining figure, the shadow of a vertical tower on the level ground increases by $10 \mathrm{m}$, when the altitude of the sun changes from $45°$ to
$30°$. Find the height of the tower and give your answer, correct to $\frac{1}{10}$ of a metre.