A single die is rolled- Probability

Question

A single die is rolled. Find the probabilities of the given events.

(a) Rolling a 4, given that the number rolled is even

(b) Rolling a 4, given that the number rolled is odd.

I know A is 1/3,but I can not figure out B

Answer 1

a) three even possibilities: 2, 4 or 6. Probability of being a 4 is 1/3

b) if number rolled is odd, it can't be 4, so probability is zero.