Hopefully this will help;
Since if you plot Vt=k r^2, the gradient of the graph will give you k, then you rearrange the formula given in the brief(the long one) to make viscosity(heta) the subject, you say you know all the values so substitute all of them and calculate to see if the viscosity matches the viscosity you know, thats stokes law proven, the only thing nagging me is that I cant imagine that the graph will give me a straight line since when y= Constant(variable^2) its normally always a parabola.