S2e this estimator of the variance of error term ?i

[Alex_Of_Darkness]

Hi everyone, it's me again... Hopefully for one last time this semester, after that I'm leaving you all alone.

So that's my sample

yi : 4, 2, 0
xi : 16, 22, 31

Already found :

​Yi + a + BXi + ?i

Also found the empirical correlation between X and Y and the R^2.

But now I need to calculate S2e which is the estimator of the variance of the error term ?i.

I calculated my ?1 = 0,1576, ?2 = -0,2632 and ?3 = 0,1056

I know that ? is the distance between Yi + a + BXi + ?i, I also know how to calculate the estimator for a variance but I'm not sure what to do here, not even sure I understand what I need to do.
Thanks a lot in advance!