Answer :
ok so the deck has 10 clubs and 10 hearts. if we pick a card, replace it, then pick again, we want to find the probability that at least one of the two cards is a heart. it's easier to first find the probability that **neither** card is a heart and then subtract from 1.
probability that the first card is a club = 10/20 = 1/2
probability that the second card is a club (since the card is replaced) = 1/2
so the probability that both cards are clubs = (1/2) * (1/2) = 1/4
therefore, the probability that at least one card is a heart = 1 - probability that both cards are clubs = 1 - 1/4 = 3/4