A thin electrical heater is wrapped around the outer surface of a long cylindrical tube whose inner surface is maintained at a temperature of 5°C. The tube wall has inner and outer radii of 25 and 75 mm, respectively, and a thermal conductivity of 10 W/m. K. The thermal contact resistance between the heater and the outer surface of the tube (per unit length of the tube) is R_t,c = 0.01 m ∙ K/W. The outer surface of the heater is exposed to a fluid with T_∞ = - 10°C and a convection coefficient of h = 100 W/m² ∙ K. Determine the heater power per unit length of tube required to maintain the heater at T_o = 25°C.