Tree diagrams question

https://www.quora.com/profile/Bravewarrior/p-160320592
Here is the question with its solution. I am stuck on part c. Some help would be greatly appreciated!

Which bit are you unsure about? The numerator is the joint probability so both green and the denominator is the probility of the second balll being green which is the sum of the two branches where the second ball is green (part b). Then its just the conditional rule.