let's notice that, each angle has an "angle tickmark", indicating that all three angles are equal, thus is an equilateral triangle, since the sides are equal, then
[tex]\bf \stackrel{AC}{4x-30}~~=~~\stackrel{CB}{2x+20}\implies 2x-30=20 \\\\\\ 2x=50\implies x = \cfrac{50}{2}\implies x=25[/tex]
