Find the surface area and volume of a sphere of diameter 21 cm.

Given, diameter = 21 cm.

Radius = $\dfrac{\text{Diameter}}{2} = \dfrac{21}{2} = 10.5$ cm.

Surface area of sphere = 4πr².

Putting values in equation we get,

$\text{Surface area of sphere } = 4 \times \dfrac{22}{7} \times (10.5)^2 \\[1em] = \dfrac{4 \times 22 \times 110.25}{7} \\[1em] = \dfrac{9702}{7} = 1386 \text{ cm}^2.$

Volume of sphere = $\dfrac{4}{3}πr^3$

Putting values in equation we get,

$\text{Volume of sphere } = \dfrac{4}{3} \times \dfrac{22}{7} \times (10.5)^3 \\[1em] = \dfrac{4 \times 22 \times 1157.625}{21} \\[1em] = \dfrac{101871}{21} \\[1em] = 4851 \text{ cm}^3.$

Hence, the surface area of sphere = 1386 cm² and volume of sphere = 4851 cm³.