The principle is that radians times the radius equals the arc length. 2pi radians = 360 degrees. You can see this principle work in the circumference formula 2pi r = C. For your problem;
The angle for arc RN in radians = 230 / 140 or 23/14 radians = 1.64286 rad
Change this to degrees as follows:
2pi / 1.64286 = X / 360 Solve for X by multiplying both sides by 360
X = 94.12878 degrees. To the nearest degree its 94 deg.