Considering the ballon to be spherical It's volume is given by 4/3(π r^3) by differentiating volume with respect to time we get rate of change of volume hence, 4πr^2(dr/dt)=600÷60=10 Substituting r=30cm 4π(30)*(30)(dr/dt)=10 dr/dt=rate of increase in bullion's radius=1/(360π)cm/s
