1.5.1 Suppose that we roll four fair six-sided dice. (a) What is the conditional probability that the first die shows $2$, conditional on the event that exactly three dice show $2$?
My attempt:
Let A be the event that first die shows 2
Let B be the event that exactly three die shows 2
There is a $\frac{1}{6}$ chance to get 2.
$|S| = 6^4$ total amount of outcomes
How do I go about this?