Hey there!
You can tell that the two angles are congruent because of the arc. So make the two angles each other.
3x-17=25-3x. Add 3x to each side. You get 6x-17=25. Add 17 to each side to get 6x=42. Divide each side by 6. You get x=7. So the value of x would be 7.
I hope this helps!