Sure! Let me help you on this one, Adrien.
There are 18 marbles in the bag, 3 of them being blue. Let's put this in a ratio.
3 out of 18.
Simplify.
1 out of 6.
This means that statistically speaking, if you pull out 6 marbles, one of them will be blue.
P.S. If this answer helped you, please, make sure to say "Thanks" just below my answer. It will help me a lot.