The marginal cost should be defined when there is a change in the revenue where the total cost leads from the production of an extra unit of output.
The marginal cost is the cost in which there is a change in total cost while producing an extra unit of output
The formula is used for computing the marginal cost is
Marginal cost = change in production cost ÷ change in quantity
By dividing the change in production cost from the change in quantity we can get the marginal cost and the same is to be considered
hence, the second option is correct.
Learn more about marginal cost here: https://brainly.com/question/24327765