So what I would do first, would be to write the probability of chosing each counter out of the bag. For example red is 3/6 => 1/2, green is 2/6 => 1/3, and blue is 1/6.
Then 5a => 1/6 is worse than even but not impossible so it is unlikely.
5b => 1/2 Well there are three red counters and six total meaning prob is 3/6 => 1/2. Hence circle a half.
5c => There are no white counters, so it is impossible!