Start with total revenue
Calculate the change in total revenue
Calculate the change in quantity sold
Divide the change in total revenue by the change in quantity sold
Use the formula: Marginal Revenue = Change in Total Revenue / Change in Quantity
For a single additional unit, compare revenue before and after selling that unit
If price changes with quantity, use the revenue from the extra unit, not the original price
If total revenue is given by a function, take the derivative with respect to quantity
Check units to ensure the result is revenue per unit
Interpret the result as the extra revenue from selling one more unit