A steady electrical current passes through a 1 cm thick slab of invar (k = 15 W/(m K)), a Ni-Fe alloy whose thermal expansion coefficient from 0 ºC to 230 ºC is lower than that of any other metallic material. The specimen's faces through which the current is passed have dimensions 12 cm x 50 cm, and are maintained at 30°C and 50°C. If the electrical resistivity of invar is 80 μΩ cm, what is the largest current (in A) that can be passed through the metal without the steady-state temperature exceeding 120°C anywhere?