A thin-walled copper tube of an outside radius of 0.01 m contains steam at 400 K and the surrounding air is at a temperature of 300 k. The tube is insulated with insulation of conductivity of 0.07 W/mk and the external convective coefficient is 4 W/m2k. Find the percentage increase in the rate of the heat transfer with a thickness of insulation with respect to no use of insulation per meter length of the tube (up to one decimal place)