9 A bag contains only red marbles and blue marbles. The number of red marbles in the bag can be represented by x. The number of blue marbles is 12 more than 3 times the number of red marbles. There are a total of 48 marbles in the bag. What is x, the number of red marbles in the bag? AS B 12 C 9 D 15 ere used create the following figure. (7.11A)