From Förberedande kurs i matematik 1

The side adjacent to the angle of \displaystyle \text{5}0^{\circ } is marked \displaystyle x and the opposite is the side of length \displaystyle \text{19}.

If we write the tangent for the angle, this gives a relation which contains \displaystyle x as the only unknown,

\displaystyle \tan 50^{\circ }=\frac{19}{x}

This gives

\displaystyle x=\frac{19}{\tan 50^{\circ }}\quad \left( \approx 15.9 \right)