Check the picture below.
since the points of tangency at N and M are right-angles, and NY = MX, then we can run an angle bisector from all the way to the center, giving us P = 30° + 30° = 60°.
now for the picture at the bottom, we have the central angles in red and green yielding 106°, running an angle bisector both ways one will hit N and the other will hit M, half of 106 is 53, so 53°, so subtracting from the overlapping central angle of 120°, 53° and 53°, we're left with b = 14°.
Now, the central angle of 120° is the same for the inner circle as well as the outer circle, so "a" takes the slack of 360° - 120° = 240°.