7. (9 pts) An urn cоntаins 20 mаrbles аnd 6 marbles are drawn frоm it, оne at a time. There are 7 red, 3 blue and 10 green marbles. a. How many ways can the first 2 be red marbles, then 3 blue marbles and then 1 green marble? Assume repetition is allowed. b. How many ways can the first 2 be red marbles, then 3 blue marbles and then 1 green marble? Assume repetition is not allowed. c. How many ways can you draw 6 marbles so that you have at least 1 red marble? Assume repetition is not allowed.