rates of change question

Stuck on this question. I formed an equation of dA/dt=dA/dr * dr/dt.
I know dA/dr is 8*pi*r. But i dont know how to work out dr/dt.

QUESTION: The volume of a sphere is decreasing at a rate of 60mm^3s^-1. Find the rate of decrease of the surface area when the volume is 800mm^3.

Stuck on this question. I formed an equation of dA/dt=dA/dr * dr/dt.
I know dA/dr is 8*pi*r. But i dont know how to work out dr/dt.

QUESTION: The volume of a sphere is decreasing at a rate of 60mm^3s^-1. Find the rate of decrease of the surface area when the volume is 800mm^3.

Note that volume of a sphere radius $r$ is $V = \dfrac{4}{3}\pi r^3$. Therefore, $\dfrac{dV}{dr} = 4\pi r^2$.

We are told that $\dfrac{dV}{dt} = -60$ hence $\dfrac{dV}{dr}\dfrac{dr}{dt} = -60$.

When $V=800$, what is $r$??

Hence, what is $\dfrac{dV}{dr}$ ?

Hence, what is $\dfrac{dr}{dt}$ ?