Two concentric steel pipes of diameters 10 cm and 15 cm (i.e. a steel pipe of inner diameter 10 cm and outer diameter 15 cm): inner fluid 600 °C (h = 35), outer fluid 15 °C (h = 500 W/m^{2}·K), k = 70 W/m·K. Calculate (a) the thermal resistance per unit length (answer in K·m/W) and (b) the heat transfer rate per unit length (answer in W/m).