Let ∠a = x. Then ∠b = x + 45°, ∠c = x − 30°.
Angles on a straight line: x + (x + 45°) + (x − 30°) = 180°.

3x + 15° = 180°
3x = 165°
x = 55°.

Fraction of 180°: \(\frac{55}{180} = \frac{11}{36}\).

Final Answer: \(\frac{11}{36}\)