There are 45 egg boxes in a store. Twenty are Brand A, fifteen are brand B, and

Question:

There are 45 egg boxes in a store. Twenty are Brand A, fifteen are brand B, and ten are Brand C. Brand A and C each have half green boxes and half yellow boxes. Brand B is all yellow.
a. If you have Brand B or C, what is the chance that you have a green box?
b. If you have a yellow box, what is the chance the brand is B?