differential equation..

the volume of sphere V = 4*pi*r³ / 3

given dV/dt = c(some constant)

so 4*pi*r² dr/dt = c.....(1)

integrating from t=0 to t=3 and r=3 to r=6. by this we can find value of c.

now integrate eq(1) from t=0 to t='t' and r=0 to r='r'

by this we can find out radius as a function of time t.