The problem is stated as follows:

You have an urn with 12 red balls, 20 green balls, and 13 yellow balls. Suppose 3 balls are drawnwithoutreplacement. What is the probability the third ball is yellow given the first ball is green.

I am pretty sure I use Bayes formula, but Im not certain how to apply it in this case. Im really just baffled! Can anyone help me?