>>48146833/sci/chad here. It's 2/3. Let me explain.
Before you taken the ball out, there are 3 red balls and 3 blue balls. Each separated in 3 boxes.
Then you take out one that's a blue ball. This eliminates the probability that it you're in the all red box. However it also eliminates one of the blue balls.
Now there are only 1 red balls and 2 blue balls left making there 3 in total. 2/3 are blue so it is 67% chance.
