A bucket is in the from of a frustum of a cone and holds 28.490 litres of water. The radii of the top and bottom are 28 cm and 21 cm respectively. Find the height of the bucket.

Answer: Option A

Volume of bucket :
= 28.490 litres
= (28.490 ×1000) cm³
= 28490 cm³
Let the height of the bucket be h cm
We have : r = 21 cm. and R = 28 cm
$$\therefore \frac{\pi }{3}h\left[{\left(28\right)}^2+{\left(21\right)}^2+28\times 21\right]$$     $$=28490$$
$$\Rightarrow h\left(784+441+588\right)=$$     $$\frac{28490\times 21}{22}$$
$$\begin{array}{rl}& \Rightarrow 1813h=27195\\ & \Rightarrow h=\frac{27195}{1813}\\ & \Rightarrow h=15cm\end{array}$$