Arc length = $\dfrac{\theta}{360} \times 2\pi r$ ⟹ $20 = \dfrac{\theta}{360} \times 2\pi \times \dfrac{60}{\pi}$ ⟹ $20 = \dfrac{\theta}{360} \times 120$ ⟹ $\theta = 60°$. Answer: (B) 60°
Use the arc length formula from the summary: $l = \dfrac{\theta}{360} \times 2\pi r$. Substitute $l = 20$ cm and $r = \dfrac{60}{\pi}$ cm — the $\pi$ cancels neatly, giving $\theta = 60°$. The key trick is noticing the radius is given as $\dfrac{60}{\pi}$ precisely so $\pi$ cancels.