Join OE and OD.
Internal angle of regular pentagon = 108^{°}
∠EAB = ∠EDC = 108^{°}
∠OAB = 60^{°}
∠EAO = 48^{°}
AO = OB = AB as the triangle is equilateral.
AB = AE as this is a regular pentagon.
Triangle AEO is isosceles as AO = EA.
∠AEO = ∠AOE = x (say)
In triangle AEO,
∠OAE + 2x = 180^{°}
48^{°} + 2x = 180^{°}
2x = 132^{°}, or x = 66^{°}
Answer choice (a)
Correct Answer: 66^{°}