A gear made of 1020 steel (0.20 wt% C) is to be gas-carburized at 927°C (1700°F). Calculate the carbon content at 0.040 in. below the surface of the gear after a 7.0-h carburizing time. Assume the carbon content at the surface of the gear is 1.15 wt%. D (C in _ iron) at 927°C = 1.28 × 10_11 m2/s.