As the problem can be modeled using a right triangle and the trigonometric functions of the inner angles.
The trigonometric function that relates the two sides of the triangle but not the hypotenuse is the tangent.
[tex]\tan (30^{\prime})=\frac{opp}{adj}[/tex]write the tan in function of the information given
[tex]\tan (30)=\frac{h}{18}[/tex]solve the equation for x
[tex]\tan (30)=\frac{\sqrt[]{3}}{3}[/tex][tex]\begin{gathered} \frac{\sqrt[]{3}}{3}=\frac{h}{18} \\ 18\cdot\frac{\sqrt[]{3}}{3}=h \\ 6\sqrt[]{3}=h \\ h=10.392\cong10ft \end{gathered}[/tex]