Exercises: sin, cos and tan

To determine the width of a river, one has marked out the distance $\overline{\mathrm{AB}}=80m$ on one bank. On the other bank, opposite $B$, there is a point $C$. The angle between $AB$ and $AC$ is measured as $\alpha ={38}^{\circ }$. First make a sketch and then calculate the width of the river.