From bag A containing 4 black and 8 blue marbles, 6 marbles are transferred into an empty bag B. Three marbles are now drawn from bag B, and each of them happens to be black.

Determine the probability that a fourth marble drawn from bag B will be black, given that:

(I) The first three marbles are returned to bag B.

(II) None of the first three marbles is returned to bag B.