On an average day, a company writes checks totaling $1,500. These checks take seven days to clear. The company receives checks totaling $1,800. These checks take four days to clear. The cost of debt is 9%. What is the firm's disbursement float?

A. $-10,500

B. $-8,700

C. $1,800

D. $10,500

E. None of the above. Please show work.