A sample space is the space of all the possible outcomes in this event.
Let's define each outcome as:
(first marble, second marble)
Where the first marble can be green or red.
The second marble can be blue or yellow.
Then the possible outcomes are:
(green, yellow)
(green, blue)
(red, yellow)
(red, blue)
So we have four different outcomes, which means that the sample space has 4 elements.
Notice that the number of marbles of each color does not affect this, these numbers only affect the probability of each one of these possible outcomes.
If you want to learn more, you can read:
https://brainly.com/question/24329720