Answer
$56^{\circ}$
Work Step by Step
The trigonometric ratios are as follows: $\sin \theta= \dfrac{opposite}{hypotenuse}$ ; $\cos \theta= \dfrac{Adjacent}{hypotenuse}$ and $\tan \theta= \dfrac{Opposite}{Adjacent}$
Since, the height of the pole= $6$
Then $\tan \theta= \dfrac{6}{4}$
So, $\theta=\tan^{-1} (\dfrac{6}{4}) =56^{\circ}$
Our required answer is (using a calculator):
$ a = 56^{\circ}$
