QUESTION $4$

$[8]$

In the diagram below $AD$ is a vertical structure. $B,C$ and $D$ are three points on the same horizontal level. The angle of elevation of A from $C$ is $.BC=k$ meter, $AB=2BC$ and $\frac{A}{b}ar(BC)=2$

$4\mathrm{.}1$ Determine the length of $AC$ in terms of $k$ and $$

$(6)$

$4\mathrm{.}2$ Hence calculate the value of $AC,$ rounded to the nearest meter, if $k=139,5$ meter and $=42$

$(2)$