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:
[tex]\tan 39^\circ = \dfrac{10}{x}[/tex]
[tex]x = \dfrac{10}{\tan 39^\circ} \approx 12.35 \textrm{ m}[/tex]
Answer B
