Formula for Glide path

Hi Experts,

I would like to ask for help on my formula. I have been looking all over the net and couldn't find anything.
I have the current scores. The green part are the month on month TARGET to get to 60.
The rising target to 60 should be increasing based on the YTD Scores.
It should have an equal distribution in terms of the increment.
The idea of this tool is we can plug any YTD Scores and it will auto populate the increasing targets. It's like a Score Calculator.
Please see attached to play around.
If anyone can share a formula on how to do this I would really appreciate it.
Test Image.PNG