data ex9_12;
  input x y c;
cards;
13    3.54    1
11    3.01    1
 9    3.09    1
 6    2.48    1
 8    2.56    1
10    3.36    1
12    3.18    1
 7    2.65    1
10    3.01    2
 9    2.83    2
11    2.92    2
12    3.09    2
15    3.98    2
16    3.89    2
 8    2.21    2
 7    2.39    2
10    2.74    2
15    3.36    2
;
proc glm;
  class c;
  model y=x c x*c;
proc glm;
  class c;
  model y=x c;
run;