Can show me step by step the derive as expression rMethanol in terms of rate constant, equilbrium constant and total concentration and pressure?

1. Consider catalytic reaction to produce methanol from methane as shown below: CH4+SCH4.SO2+S2OSCH4S+O.SCH3OH+2S Assuming that step (3) is the rate limiting step, derive an expression rmethanol in terms of rate constant, equilibrium constant, total concentration and pressure Pi