Q$3)$ FLOW IN A PIPE

Pure water at $30C$ flows at a velocity of $0\mathrm{.}04\frac{m}{s}$ in a tube having an inside diameter of

$6mm.$ The tube is $2\mathrm{.}0m$ long, and the inside wall of the tube is coated with benzoic acid.

Assuming the flow is fully developed in the tube, what is the concentration of benzoic

acid at the outlet?