A double$-$pipe heat exchanger is constructed of a copper $($k $=380$ W$/$mK$)$ inner tube of internal diameter Di $=2\mathrm{.}2$ cm and external diameter Do $=2\mathrm{.}6$ cm and an outer tube of diameter $3\mathrm{.}0$ cm$.$ The convection heat transfer coefficient is reported to be hi $=700$ W$/$m$2$K on the inner surface of the tube and ho $=2800$ W$/$m$2$K on its outer surface. For a fouling factor Rf$,$ i $=0\mathrm{.}0005$ m$2$K$/$W on the tube side and Rf$,$ o $=0\mathrm{.}0002$ m$2$K$/$W on the shell side$\mathrm{.}1)$ Determine the thermal resistance of the heat exchanger per unit length. $($Round the answer to five decimal places.$)2)$ The thermal resistance of the heat exchanger per unit length is $0\mathrm{.}0623$C$/$W$.$ Calculate the overall heat transfer coefficients Ui and Uo based on the inner and outer surface areas of the tube, respectively.