Consider the following situation, where a liquid of density $1000k\frac{g}{m^3}$ and viscosity $0\mathrm{.}001$

$N\frac{s}{m^2}$ is inside a container. There is an impeller at the bottom of the container below the

top surface of liquid$)$ that rotates very slowly. The impeler imparts momentum to the fluid that

diffuses upward. At the top of the liquid is a thin layer of ink, which moves downward with a

mass diffusivity of ${10}^{-6}\frac{m^2}{s}.$ After how much time will the diffusion front of the ink and that of

the momentum meet each other?