Sum of the squared least squared residual

#1
Hey guys!
This is my first post on this booming forum!
I came across a problem that asks "Find the Sum of the squared least squared residual" and All it gives is sigma squared hat and the population and I have searched through the book and I have no idea where to start or what formulas to use. I was hoping that someone could give me some guidance about where to start.Thank you in advance!