Question

Find the missing side. It’s trigonometry, and I’ve tried this 5 times.

Answer 1

That triangle's upside down but the usual rules hold.

We know the side opposite the 39 degree angle is 10 m and we're asked for the adjacent side.  The unlabeled side is the hypotenuse.

That's tangent:

$\tan 39^\circ = \dfrac{10}{x}$

$x = \dfrac{10}{\tan 39^\circ} \approx 12.35 \textrm{ m}$

Answer B