What is the length of AB?

As you can see from the diagram, this is an isosceles triangle (triangle where 2 sides are equal and angles opposite are also equal).
Since there are two 65 degree angles, the sides opposite them are also equal. So we can write:
[tex]6x=3x+9[/tex]
Solving for x:
[tex]6x=3x+9\\6x-3x=9\\3x=9\\x=\frac{9}{3}\\x=3[/tex]
Now, we want to know side length of AB, which is 6x. Plugging in x = 3 into that, we get:
[tex]AB=6(3)\\AB=18[/tex]
Answer choice D is right.
ANSWER: D