A balloon is being inflated,the radius of the balloon,initially zero,increases at the rate of 9 ft/sec.How fast is the volume increasing after 1/2 second?

Answer 1

V = (4/3) π r^3
dV/dt = 4πr^2 dr/dt

after 1/2 second, the radius is 4.5 ft

back in dV/dt
= 4π(4.5)^2 (9) = ....