How do I find the predictors from this equation in this form?

I am having trouble understanding how to find the predictors of this regression model.

y=x1β1+x2β2+E

I need to find it in the form: n ∑= x^2i1 i=1

Again I know how to normally find the beta predictors but this form that I have to find it in is confusing me.

(I need to do this by hand so please don't ask about programming it)