In a circle of radius 21 cm, an arc subtends an angle of 60°

Let ACB be the given arc subtending at an angle of 60°">60° at the centre.
Now, we have:

$r=21 \mathrm{~cm}$ and $\theta=60^{\circ}$

$\therefore$ Length of the $\operatorname{arc} \mathrm{ACB}=\frac{2 \pi r}{360}$

$=\left(2 \times \frac{22}{7} \times 21 \times \frac{60}{360}\right)$

$=22 \mathrm{~cm}$