V = 3, Please help asap! Thank you very much

Question 2) a) Cite two diffusion mechanism in crystalline solids, and using schematic representation explain how these mechanisms function. (4pts) b) A sheet of steel 1.5 mm thick has nitrogen atmospheres on both sides at 1200C and is permitted to achieve a steady-state diffusion condition. The diffusion coefficient for nitrogen in steel at this temperature is 6 x10-11 m/s, and the diffusion flux is found to be 1.V x 10-7 kg/m2-s. Also, it is known that the concentration of nitrogen in the steel at the high-pressure surface is 4 kg/m. How far into the sheet from this high-pressure side will the concentration be 2.0 kg/m??. (8pts) (V is the last digit your registration number)