An iron slab and a copper slab having rectangular cross-sections and identical dimensions are welded together end to end. The outer ends of iron and copper slabs are held at 0^ C and 100^ C respectively. The thermal conductivities of iron and coppes are 80 ~W ~m ⁻¹ ~K ⁻¹ and 400 ~W ~m ⁻¹ ~K ⁻¹ , respectively. Then, ignoring convective and radiative losses, the temperature of the junction is close to