We have to find the length of AC.
As we have a right triangle of which we know the length of the hypotenuse and one angle measure, we can use a trigonometric ratio to find AC:
[tex]\begin{gathered} \sin (B)=\frac{\text{Opposite}}{\text{Hypotenuse}}=\frac{AC}{BC} \\ AC=BC\cdot\sin (B) \\ AC=18\cdot\sin (30\degree) \\ AC=18\cdot\frac{1}{2} \\ AC=9 \end{gathered}[/tex]
Answer: AC = 9
