powerbi – How to calculate roll up summary using dax

Hi I have a dataset like this, the date difference between each sprint is 14 days.

DateBegin   Sprint   Points
1/2/2021    Sprint1   30
1/16/2021   Sprint2   40
1/30/2021   Sprint3   20
2/13/2021   Sprint4   70
2/27/2021   Sprint5   90
3/11/2021   Sprint6   55
3/25/2021   Sprint7   40

I wanted to calculate the Sum average using the last 3 sprints.
for example

for Sprint7- sum(Sprint6+Sprint5+Sprint4)/3
For Sprint6- sum(Sprint5+Sprint4+Sprint3)/3

Something like For each Sprint look up the last 3 sprints and Sum them up and take the average(measure).