A realtor sold a house on August 31, 2011, for $150,000 to a buyer in which a 20% down payment was made. The buyer took a 15-year mortgage on the property with an effective interest rate of 8% per annum. The buyer intends to pay off the mortgage owed in yearly payments starting on August 31, 2012. (a) How much of the mortgage will still be owed after the payment due on August 31, 2018, has been made? (b) Solve the same problem by separating the interest and the principal amounts.