Find the perimeter of a semicircular plate of radius 3.85 cm.

Perimeter of semicircular plate = (π + 2)r

$= \Big(\dfrac{22}{7} + 2\Big) \times 3.85 \\[1em] = \Big(\dfrac{22 + 14}{7} \Big) \times 3.85 \\[1em] = \dfrac{36}{7} \times 3.85 \\[1em] = 36 \times 0.55 \\[1em] = 19.8 \text{ cm}.$

Hence, perimeter of a semicircular plate = 19.8 cm.