On Average, Your Firm Receives 50 Checks a Day from Customers

On average, your firm receives 50 checks a day from customers. These checks, on average, are worth $20 each and clear the bank in 4 days. In addition, your firm mails out 40 checks a day with an average amount of $30. These checks clear your bank in 3 days. What is the average amount of the collection float?

A) $1,000
B) $3,600
C) $4,000
D) $4,500
E) $6,000