(a) If four cards are taken at random from a pack of cards without replacement, what is the probability of having exactly two hearts?
(b) If four cards are taken at random from a pack of cards without replacement, what is the probability of having exactly two hearts and exactly two clubs?
(c) If four cards are taken at random from a pack of cards without replacement and it is known that there are no clubs, what is the probability that there are exactly three hearts?