(a) Not enough information - we don't have figure for the total number of marbles (though we have the number taken out) - so there is no way to figure the number not chosen.

(b) The number of red marbles chosen: =16-number of blues 16-16*5/8=16 - 10= 6

(c) Not enough information. We don't know how many red marbles in total were in the bag before selection.