Answer: (Don't read this if this is a test)
Step-by-step explanation: I might get this wrong because I was kind of confused too (sorry if I am!)
Hello! The first thing you would want to do for these kinds of questions is to write the probability of a green, blue, or red marker being picked as a fraction. To do this, add 12 + 4 + 20 which is 36.
The probability of picking a green marker - 12/36, partially simplified = 3/9
The probability of picking a blue marker - 4/36, simplified = 1/9
The probability of picking a red marker - 20/36, simplified = 5/9
G - 3/9
B = 1/9
R = 5/9
You know that the probability of picking a blue marker is 1/9. Once you know this, you can figure out the new probability of picking a red marker since the blue marker won't be replaced. The answer is 4/35. Multiply 1/9 by 4/35 to find the probability of picking one after the other and you will get 4/315.