$(10$ pt$.$ @ $5$ pt$.$ each$)$ Water is flowing at the rate $50\frac{m^3}{m}in$ from a shallow concrete conical reservoir $($vertex down$)$ of base radius $45$ meters and height $6$ meters.

a$.$ How fast $($centimeters per minute$)$ is the water level falling when the water is $5$ meters deep? Round your final answer to hundredths.

b$.$ How fast is the radius of the water's surface changing then? Answer in centimeters per minute. Round your final answer to hundredths.