How do you solve this?

Problem 3 (25 points) Certain bioreactors use spherical particles coated with stem cells and suspended in a liquid solution, with the reactor tank constantly stirred by an impeller. The impeller should rotate just fast enough to keep all the particles suspended-any faster and the stem cells might be damaged. This rotation rate is the "just-suspended agitation rate," Njs (units = rotations/time). Suppose Njs is known to depend on the impeller diameter D, the density and viscosity of the liquid (,), and gravity (g). You want to predict Njs for a bioreactor using a model reactor at 1/2 scale. If the full-sized bio-reactor is to be filled with water, what must the kinematic viscosity (or ratio of viscosity to density / ) of the liquid inside the model reactor be for the two systems to be fully similar? If the model is filled with such a liquid and its just-suspended agitation rate is then measured to be 1s1, what should be the rotation rate of the full-sized reactor