During the past 6 months, 15 of an Australian-based companys customers have left to do business with one of its competitors. During the same time, the company has started doing business with 25 new customers. The average revenue that outgoing customers generated was $1000. The average revenue that new customers generate was $500. How many more customers generating the average revenue for new customers does the company need to account for the difference between the revenue for ongoing and new customers?