Humphrey's Housing has been practicing cash management for some time by using the Baumol model for determining cash balances. Some time ago, the model called for an average balance (C*/2) of $600; at that time, the rate on marketable securities was 4 percent. A rapid increase in interest rates has driven the interest rate up to 9 percent. What is the appropriate average cash balance now?

a. $267 b. $333 c. $400 d. $533 e. $800