Answer to Problem # 19:Make a simple matrix table:NOWTHENJOE 24 Old as Bill is (Y) BILL Y ½ Joe's age now (12) Joe's age minus Bill's age remains constant(Difference now = Difference then)24 - Y = Y - 12 or 2Y = 36 Y = 18 (Bill's age) (ANSWER)'Then' is 6 years ago when Joe was 18 (as old as Bill is now)return