Answer: 1/3
Step-by-step explanation:
"given it is an even number" tells us that the outcomes could be anything from this set {2,4,6}. We ignore the odd numbers entirely.
We have one copy of "6" out of three total items.
Therefore, we end up with a probability of 1/3
This is approximately equal to the decimal form 0.333 and the percent form 33.3%
I would stick to the fraction form since it's most exact. However, if your teacher instructs otherwise then be sure to follow said instructions of course.