1) We have that there are (52,3) ways to pick 3 cards out of 52 cards. Also, there are (4,3) ways to pick 3 kings out of the 4 total available kings in the deck. In essence, we need to have one of those ways to be the selected 3 cards. Hence, the probability is the ration (4,3)/(52,3). Computing this:
P=

The probability is very low but not negligible.
2) The Pascal triangle defines a recursive relationship. Hence, we would need to calculate all the binomial coefficients up to 51. Thus, it is not at all practical to use the Pascal Triangle to calculate the ways. It is easier to do the direct computation.