Two stainless steel plates (p = 8000 kg/m³, c = 500 J/kg ∙ K, k = 15 W/m ∙ K), each 20 mm thick and insulated on one surface, are initially at 400 and 300 K when they are pressed together at their uninsulated surfaces. What is the temperature of the insulated surface of the hot plate after 1 min has elapsed?