Answer: The inequality that represents this situation is:
Let's break it down:
The term "2400" represents the earnings from existing customers.
The term "125x" represents the earnings from new customers, where x is the number of new customers.
The inequality "2400 + 125x > 3000" states that the total earnings from existing customers and new customers combined should be greater than $3000.
Therefore, option 3, 2400 + 125x > 3000, is the correct inequality representation of the situation.