The nozzle of an experimental rocket motor is fabricated from 5 mm-thick alloy steel. The combustion gases are at 210 K, and the effective heat transfer coefficient is 6000 W/m^2K. If the nozzle is initially at 300 K and the maximum allowable operating temperature for the steel is specified as 1300 K, what is the allowable duration of firing? To obtain a conservative estimate, neglect the heat loss from the outer surface of the nozzle. Take k = 43 W/mK, a = 12.0x10^-6 m^2/s for the steel.