A rectangular plate of width $0\mathrm{.}5$ m and length $0\mathrm{.}9$ m is dragged at a constant velocity of $0\mathrm{.}1$ m$/$s across the top surface of a layer of oil. The oil rests on a stationary flat surface, and the thickness of the oil layer is $1$ mm$.$ The force required to maintain this constant velocity is measured to be $10$ N$.$

What is the dynamic viscosity $($u $)$ of the oil in$?$