Again the answer is $3\mathrm{.}16$m$/$s

A hydraulic oil is flowing in a steel tube with an outside diameter of $2$ in and a wall thickness of $0\mathrm{.}083$ in $.$ A pressure drop of $68$ kPa is observed between two points in the tube, $30$ m apart. The oil has a specific gravity of $0\mathrm{.}90$ and a dynamic viscosity of $3\mathrm{.}0{10}^{-3}Pa*s.$ Assume the tube wall roughness to be $3{10}^{-5}m.$ Calculate the velocity of flow of oil.