Here is the question

I inflate a spherical balloon by blowing 1000cm^3 of air into it every 5 seconds.

a/ what is the rate of change of the volume of the balloon (in cm^3/sec), at the moment when the radius of the balloon is 5cm?

b/ what is the rate of change of the radius of the balloon (in cm/sec), at the moment when the radius of the balloon is 5cm?

So the Dv/Dt is (-200cm^3/sec) right? Then what?

Please Help!!