(a)[4]
From $P$, $Q$ lies on a bearing of $052^\circ$. The lengths are $PQ = 11.5\text{ km}$, $QR = 14.6\text{ km}$ and $PR = 17.2\text{ km}$. Calculate the bearing of $R$ from $Q$.
(b)[3]
$A$ is a point on level ground. The angle of elevation of the top of a vertical mast as seen from $A$ is $68^\circ$, accurate to the nearest degree. The distance from $A$ to the base of the mast is $45\text{ m}$, accurate to the nearest metre. Calculate the lower bound for the height of the mast.