The surface of a steel gear of 1022 steel (0.22 wt % C ) is to be gas-carburized at 927 ^o C. Calculate the time necessary to increase the carbon content to 0.3 wt% at 0.015 in. below the surface of the gear. Assume the carbon content of the surface to be 1.20wt%. D (C in iron ) at 927 ^o C = 1.28 x 10 ^-11 m ² /s. The answer should have one decimal of accuracy and be in minutes.