The numerator will be the number of cards that count as a "success" in your exercise. Here, that number is 8, because there are 4 aces and 4 kings.
The denominator will be the total number of cards in the deck. This number is 52, including all the aces and kings.
The denominator will be the total number of cards in the deck. This number is 52, including all the aces and kings.
Probability = 8 / 52 = 15.4%.