Of two long rods that are equivalent in every respect, except that one is fabricated from a standard material of known thermal conductivity kA while the other is fabricated from the material whose thermal conductivity kB is desired. Both rods are attached at one end to a heat source of fixed temperature Tb, are exposed to a fluid of temperature T[infinity], and are instrumented with thermocouples to measure the temperature at a fixed distance x1 from the heat source. If the standard material is aluminum, with kA = 180 W/m ⋅ K, and measurements reveal values of TA = 77°C and TB = 62°C at x1 for Tb = 100°C and T[infinity] = 25°C, what is the thermal conductivity kB of the test material?