A conical container of base radius 31cm and height 30cm is held with the vertex down to enable to water capacity. Calculate the depth of water in the tin.

The base radius of the conical container is $r_c = 21 \text{ cm}$.
The height of the conical container is $h_c = 30 \text{ cm}$.

The formula for the volume of a cone is $V_c = \frac{1}{3}\pi r_c^2 h_c$.

The radius of the cylindrical container is $r_{cyl} = 7 \text{ cm}$.
Let the depth of water in the cylinder be $h_{cyl}$.

When the water from the cone is emptied into the cylinder, the volume of water remains the same.
The formula for the volume of water in the cylinder is $V_{cyl} = \pi r_{cyl}^2 h_{cyl}$.
So, $V_{cyl} = V_c$.

Divide both sides by $\pi$:

The depth of water in the cylinder is $\textbf{90 cm}$.