rate of change- calculus worded question

*Air is being pumped into a spherical ballon so that its volume increases at a rate of 80pi cm^3/s/ How fast is the radius, r, increasing when r=2? (you may find it useful to know the volume of a sphere of radius r is given by V=4/3 pi r^3)*

Been trying to figure this out for ages and no luck at all doing these worded calculus questions and I gotta figure out how to do them for tomorrow exam (first uni maths exam ever for me!)!!

If anyone could help it would be fantastic! :)