Over the course of a day, fans pour into a NASCAR venue at the rate of 8,000 people per hour. The average rate at which fans leave the venue .

Must be exactly 8,000 people per hour.

Explanation:

Flow rate or throughput is the rate at which customers, goods, or services flow though a business process. It is usually measured as an average number of units that pass through a process per unit time.

In this scenario the people that entered the NASCAR venue were 8,000 people per hour.

So when people are coming out of the NASCAR venue average rate of flow out must be 8,000 people per hour.

The rate of units entering a business process must be equal to rate of units coming out per unit time.