Answer:
First: P, R. Second: 3.
Explanation:
In this, you can see the first tree diagram with C,R C,B and C,W.
Then when you go to the other diagram it's P,R P,B and P,W.
Therefore the combination P,R is missing from the tree diagram and belongs to the box.
When you count the number of combinations:
1, P,R
2, P,B
3, P,W
Therefore they are a total of 3 combinations.