$A$ $4 \, m$ long ladder leans on a wall such that its lower end remains $2 \, m$ away from the base of the wall. Then,the ladder makes an angle of measure $\ldots \ldots$ with the ground. (in $^\circ$)

When the angle of elevation of the sun is $30^{\circ}$,the length of the shadow of a tower is $90\, m$. Find the height of the tower. (in $m$)

$A$ pole stands vertically on the ground. The length of the shadow of the pole is $\frac{1}{\sqrt{3}}$ times the height of the pole. Then,the angle of elevation of the sun is $\ldots \ldots \ldots \ldots . . .$ (in $^\circ$)

As observed from the top of a lighthouse,the angles of depression of two ships $P$ and $Q$ anchored in the sea on the same side are found to be $35^{\circ}$ and $50^{\circ}$ respectively. Then,from the lighthouse:

Watching from the top of a tower,the angles of depression of two houses $A$ and $B$ are found to be $25^{\circ}$ and $40^{\circ}$ respectively. Then,.......

Two boats are anchored in the same direction from a $100 \, m$ high lighthouse. The angles of depression of the boats from the top of the lighthouse are $30^{\circ}$ and $45^{\circ}$. Find the distance between these two boats (in $m$).