Perimeter of sector = Arc length + 2r
Arc length = $\dfrac{60}{360} \times 2 \times \dfrac{22}{7} \times 21 = 22$ cm
Perimeter = $22 + 2 \times 21 = 22 + 42 = \mathbf{64}$ cm → Option C
Students often confuse "perimeter of sector" with just the arc length. Perimeter includes arc length + two radii. Use the formula: Arc length = $\frac{\theta}{360} \times 2\pi r$, then add $2r$. Here: arc = 22 cm, two radii = 42 cm, total = 64 cm.