We need to know the number of favourable outcomes.
The black cards are half of the deck, thus there are 26 black cards
Now there is 12 face cards in a deck. But, half of them are black, which we have already take count of them. There is 6 red face cards.
Then, the number of favourable outcomes is 26 for the black cards, plus 6 for the red face cards:
Now, to calculate the probabilities we need to divide the favourable outcomes by the total outcomes:
The probability of the even is 8/13