The chain rule question

A funnel has a circular top of diameter 20cm and a height of 30cm. When the depth of liquid in the funnel is 15cm, the liquid is dripping from the funnel at a rate of 0.2cm^3 s^-1. At which rate is the dept of the liquid in the funnel decreasing at this instant?

I have done:
dx/dt = 0.2 when x = 15cm

A funnel has a circular top of diameter 20cm and a height of 30cm. When the depth of liquid in the funnel is 15cm, the liquid is dripping from the funnel at a rate of 0.2cm^3 s^-1. At which rate is the dept of the liquid in the funnel decreasing at this instant?

I have done:
dx/dt = 0.2 when x = 15cm

What is $x$?? Define your variables first before using them.

Let $h$ be the depth of the liquid, and $t$ be the time in seconds. Then we want to find $\frac{dh}{dt}$.

Let $x$ denote the volume of liquid at a given time. Then we know at some point, we have $\frac{dx}{dt}=0.2$.

However, note that by the chain rule, we have $\frac{dh}{dx} \cdot \frac{dx}{dt}=\frac{dh}{dt}$

So you want to find $\frac{dh}{dx}$ which is the rate of change of the depth w.r.t the volume at the given time.

Hi, i followed what you were saying up until the bit where i have to find dh/dt. How do i find dh/dt? Do i have to differentiate the volume or the surface area of the sphere to find this?