John has seven red marbles and three blue marbles in a bag. He removes a marble at random, records the color, puts it back, and then repeats this process until he has withdrawn six marbles. What is the probability that exactly three of the marbles that he removes are red? Express your answer as a decimal rounded to the nearest thousandth.
Also an explanation is more helpful than just an answer, I would appreciate it if you took the extra time to help :)