In the question, the angles proves that this triangle is an isoceles triangle.
So we can set the two sides equal: [tex]x + 4 = 3x - 8[/tex]
Add [tex]-x+8 [/tex] to both sides of the equation: [tex]12 = 2x[/tex]
Divide both sides by 2: [tex]x = 6[/tex]
We find that [tex]x=6[/tex]. AC is also x, so, it is 6 too.
