this is the question of engineering material

Q #5 A material has been heat treated under a carbon environment for 5 hrs, which raises the carbon concentration to 0.5 wt% at a point 5.0 mm from the surface. How much time is required to get the same concentration at a point lcm from the surface at the same temperature for an identical material? [C3-CLO2-PLO1; 10 Marks]