options ps=54 ls=80;

data txtemp;
infile 'texas1.dat';
input county 1-15 jantemp 24-25 lat 27-33 long 35-41 elev 43-48;
lat_elev=lat*elev;
run;

proc reg;
model jantemp=lat long elev;
model jantemp=lat;
model jantemp=lat elev;
model jantemp=lat elev lat_elev;
run;

quit;