A jar contains 3 red marbles, 6 blue marbles, 5 green marbles and 6 yellow marbles. Assume there is replacement.

I believe the answer would be 36/400, 9/100, or 9%

(I believe you are asking for the probability of picking blue then another blue )

So, in the jar, there are 20 marbles, 6 of which are blue, so pick one would be a 6/20 or 3/10 ≈ 33.3%

Assuming that you grabbed a blue marble then it was replaced with another blue marble, you would multiply 6/20 and 6/20 (the individual chances of getting one blue) and get 36/400, which simplifies to 9/100 or 9%

Please correct me if I am wrong, have a good day!