Chords and arcs: find the value of x

The answer is probably 14, but I don't know how to prove it correctly, I mean by using the mathematical language. So if it will work, I can try to guess how I got this answer. So if you will draw radiuses, like I did on the screenshot, you will get 2 equal to each other triangles, but the thing is that I have no idea why they should be equal. So if the first step is right the value of x should be equal to 14, as the side below is equal to 14 too. That's it, I guess I helped you at least a little!

is this part of a question or something