Explanation:

As per the question,
It is given that, height (h) =21cm, radius (R)=5cm and (r)=3cm
$$\pi = \frac{22}{7}$$
We know that the volume of the frustum of the cone $$V=\dfrac{\pi h(R^2+r^2+R\times r)}{3}$$
$$\Rightarrow V=\dfrac{22 \times 21(5^2+3^2+5\times 3)}{3 \times 7}$$
$$\Rightarrow V=\dfrac{22 \times 21(25+9+15)}{21}$$
$$\Rightarrow V=1078 cm^3$$