Explanation:

- Two equal arcs mean the arc length is the same for both circles.

- Arc length = Radius × Angle in radians.

- Let \( r_1 \) be the radius of circle C¹ and \( r_2 \) be the radius of circle C².

- The angle at the center for C¹ is 60 degrees, and for C² is 75 degrees.

- Convert angles to radians: 60 degrees = \( \frac{\pi}{3} \), and 75 degrees = \( \frac{5\pi}{12} \).

- For equal arcs: \( r_1 \times \frac{\pi}{3} = r_2 \times \frac{5\pi}{12} \).

- Simplifying, we get \( \frac{r_1}{r_2} = \frac{5}{4} \).

- The correct option is 5:4.