Billy McMahon is interested in buying a waterfront vacation condo and has saved $100,000 for the down payment. His plans call for making additional monthly deposits into an investment account over the next 12 months. Billy McMahon wants to make the purchase 18 months from today and wants to have $240,000 saved up for the down payment. a. What is the amount of each of the additional payments he must make for his plan to work out? Assume Billy can earn 2% annual return i his investment account. nortone at 4%. what will his