$1.$A circular tube of outer diameter $5$cm and inner diameter $4$ cm is used to convey hot fluid. The inner surface of the wall of the tube is at a temperature of $80$DegC while the outer surface of the wall of the tube is at $25$DegC. What is the rate of heat transport across the tube wall per meter length of the tube at steady state, if the thermal conductivity of the tube wall is $10$ W$/($m$-$K$)?$