To solve the problem, we use the Inscribed Angle Theorem, which states that the central angle subtended by an arc is twice the inscribed angle subtended by the same arc.

Key Observations:

• Let (O) be the center of the circle, with points (A, B, C) on the circumference.
• The central angle (\angle AOB = 120^\circ) subtends arc (AB).
• For any point (C) on the major arc (AB) (opposite the center relative to arc (AB)), the inscribed angle (\angle ACB) is half the central angle.

Calculation:

[ \angle ACB = \frac{1}{2} \times \angle AOB = \frac{1}{2} \times 120^\circ = 60^\circ ]

Answer: (\boxed{60})

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