FERTIL3 for this exercise. $ (i) Regress gfr on t and t2 and save the residuals. This gives a detrended gfr , say, gf . $t 2tt (ii) Regress gft on all of the variables in equation (10.35), including t and t . Compare the R-squared with that from (10.35). What do you conclude? (iii) Reestimate equation (10.35) but add t3 to the equation. Is this additional term statistically significant? (Show code in STATA)