$4$ A rectangular conduit $200$ cm in length is needed to convey water at a fow rate of $18$ mL s$1.$ The conduit cross section has a height of $0\mathrm{.}23$ cm and a width of $0\mathrm{.}45$ cm$.$ Calculate the pressure drop $($mmHg$)$ over the length of the conduit to obtain this fow rate. Assume the kinematic viscosity $()$ of water is $0\mathrm{.}01$ cm$2$ s$1$ and its density is $1$ g cm$3.$