Percentage of Previous Record for FY group

[Cores]

Crystal Reports for Enterprise
Dear Experts,
I would appreciate if you can help!
How to create Percentage of Previous Record for FY group?
Here's a sample of data. The entries with stars are latest in FY. Selection Group Filter: Activity Date= Maximum(Activity_Date, Fiscal Year).
Region1
Activity_Date Activity_Count
2017/01/31 41
2017/02/28 43
2017/03/31 46**
2017/04/30 40
2017/12/31 52
2018/01/28 42
2018/03/31 48**
2018/04/30 47
Region2
2017/01/31 41
2017/02/28 43
2017/03/31 47**
2017/04/30 40
2017/12/31 52
2018/01/28 42
2018/03/31 54**
2018/04/30 47

We need:
- Find values when Maximum FY date: 46, 48, 47, 54, etc.
- Summarize values by FY for all regions: 2017:46+47=93 (Previous), 2018:48+54=102 (Current)
- Create formula Percentage of Previous Record for FY group: (102-93)/93*100