Answer
$23$ cm
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, $\theta=61^{\circ}$
Then $\sin 61^{\circ}= \dfrac{20}{c}$
So, $ c =20 \times \csc 61^{\circ}$
Our required answer is: $ c \approx 23$ cm
