Answer
$42$ mm
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, $\theta=23^{\circ}$
Then $\tan 23^{\circ}= \dfrac{a}{100}$
So, $ a =100 \times \tan 23^{\circ}$
Our required answer is: $ a \approx 42$ mm
