Differentiate average revenue and marginal revenue?

Average Revenue:

Total revenue divided by the number of units sold.

Marginal Revenue:

Is the extra revenue that an additional unit of product will bring. It is the additional income from selling one more unit of a good; sometimes equal to price. It can also be described as the change in total revenue ÷ the change in the number of units sold.

Relationship:

They both are the revenue brought in by, in this case, units sold. They are both used to calculate the total revenue just that marginal is any exrta revenue that the average revenue has left over.