Patty went to a dinner celebrating the wedding anniversary of her aunt and uncle. She asked her aunt how long they’ve been married. She replied, “If you can guess the magic number of years we’ve been married, we will give you a prize money of 300 times that magic number.” And then she gave this clue: Double the magic number and add 1, and then subtract 20 from the result. Add the sum of -18 and 5, and get the additive inverse of the result. You will end up with the number .