options ls=80;

data power;
input y x1 x2;
cards;
150 .6 10
86 1 10
49 1.4 10 
288 .6 20
157 1 20
131 1 20
184 1 20
109 1.4 20
279 .6 30
235 1 30
224 1.4 30
;
proc means data=power;

*define centered variables;         

data b; set power;
x1p=(x1-1.0)/0.4;
x2p=(x2-20)/10;

data b; set b;
x1psq=x1p*x1p;
x2psq=x2p*x2p;
x1px2p=x1p*x2p;

proc reg data=b;
  model y= x1p x2p x1psq x2psq x1px2p;
  model y= x1p x2p;                   
run;