In a circle of radius $\displaystyle 21$ cm , an arc subtends an angle of $\displaystyle 60^{\circ}$ at the centre. Find the area of the sector formed by the arc. Also, find the length of the arc.

\[\begin{aligned} & A=\frac{60}{360} \times \frac{22}{7} \times 21 \times 21=231 \mathrm{~cm}^{2} \\ & \begin{aligned} \text { Length of arc } & =\frac{60}{360} \times 2 \times \frac{22}{7} \times 21 \\ & =22 \mathrm{~cm} \end{aligned} \end{aligned} \]