Heat transfer by Holman, this question is from chapter 2

The thermal conductivity for steel from table A-2 is (54 W/m.C)

Q2. The inside temperature of steel cylinder (Dr4cm. Do =5cm) is maintained at 120C and exposed to a convection environment with T=20 and h=50W/m2C. Calculate the thermal conductivity that will just cause an insulation thickness of 0.4mm to produce a twice of the critical madius How much of this insulation must be added to reduce the heat transfer by 60 percent from that which would be experienced by the uninsulated cylider? How much heat is ost after insulation