We have a fair number cube.
This means that each roll, we have equal chances of getting a number from 1 to 6.
In this case, we want to know the probability of getting a 5 given that he has rolled an even number.
As 5 is an odd number, "getting a 5" and "getting an even number" are mutually exclusive events.
Then, if one is given, the other can not happen (as only one of the mutually exclusive events can happen), so it has a probability of 0.
Answer: the probability of a 5, given that he roll an even number, is 0.