Question

A spherical helium balloon has a diameter of 30 cm. How much helium is needed to fill the balloon, in cubic centimeters? Round your answer to the nearest centimeter

Answer 1

From V= 4/3*pi*r^3 
dV/dt = 4pi(r^2)dr/dt 
so when dV/dt=30 and r = 19 
30 = 4pi(361)dr/dt 
dr/dt = 30/[4pi(361)] 

now in 
A = 4pir^2 
dA/dt = 8pi(r)dr/dt 
= 8pi(19)*30/[4pi(361)] 
= you finish it.
HOPE THIS HELPS.