Bill made a budget and planned to deposit $150 a month in a savings account, beginning September 1. He did this, but on the following January 1, he reduced the monthly deposits to $100 a month. In all he made 18 deposits, four at $150 and 14 at $100, if the savings account paid 6% interest, compounded monthly, what was the future worth of his savings account immediately after he made the last deposit?