Difference between rows for A/B test

[reachbgk-162385]

I am trying to build a dashboard to assess performance of A/B test (test vs control group) for campaigns. This is how my data is :

How do I get % change between test and control groups of Campaign C1, C2 etc. Note that not every campaign has a test and control group.

I have sorted my data based on campaign and group. In simple English what I want to do is “if a campaign has test and control then calculate the % difference in the number of clicks between the two groups”

Any idea how to do this ?

campaign	group	clicks
C1	test	10
C1	control	2
C2	control	5
C3	test	20
C4	test	15
C4	control	25