I had to "draw a picture" to understand this one . . .
There are, of course, 52 cards in the deck.How many ways are there to choose 4 cards of different suits
and different values from a deck of 52 cards?
The first card can be any of the 52 cards.
. . Suppose it is
Then these choices remain for the second card:
There are 36 choices for the second card.
Suppose the second card is
Then these choices remain for the third card:
There are 22 choices for the third card.
Suppose the third card is
Then these choices remain for the fourth card:
There are 10 choices for the fourth card.
Disgarding the order in which the four cards are drawn,
. . there are: . such 4-card hands.