A bag contains 2 white marbles abd six black marbles.

a. Find the probability of picking out 2 black marbles in a row if the first marble is returned to the bag before the next marble is picked.

b. Find the probability of picking two black marbles in a row if the first marble is not returned to the bag before the next marble is picked.

c. Find the probability of picking out a white marble, then a black marble if the first marble is not returned to the bag.