use caschool, clear
drop in 101/420
regress testscr str el_pct avginc comp_stu expn_stu 
predict yhat, xb
di e(rss)

regress testscr str el_pct avginc 
predict ehat, residual

regress expn_stu str el_pct avginc 
predict e1, residual

regress comp_stu str el_pct avginc
predict e2, residual

* g
regress ehat e1 e2, noconstant
di e(rss)

* h
regress ehat str el_pct avginc e1 e2
di e(rss)

* i
regress ehat e1 e2, noconstant
di e(rss)

*j
regress yhat e1 e2, noconstant
di e(rss)