To solve this problem you must apply the proccedure shown below:
1. Let's divide the triangle in two right triangles. Now, you must find the height and the base of the triangle on the left, as below:
Sin(60°)=h/9
h=(9)(Sin(60°)
h=(9√3)/2
h=7.79
Cos(60°)=b/9
b=9/2
b=4.5
3. Now you can calculate the value of x, which is the hypotenuse of the triangle on the right, by applying the Pythagorean Theorem. You have that its base is:
Base=18-4.5=27/2=13.5
x=√(13.5)^2+(7.79)^2
x=15.58
x=9√3
The answer is: D. 9√3