SAS如何进行协方差分析？

如果这个题目以x作为协变量该怎么写呢？谢谢。
data covariate;
input percent $ x y;
datalines;
2.5% 6.5 7.1
2.5% 5.9 6.8
2.5% 7 7.8
2.5% 6.3 7
2.5% 7 8.1
2.5% 6.7 7.4
2.5% 7 7.8
2.5% 7.1 8.1
2.5% 6.1 7
2.5% 6.6 7.4
5.0% 7.1 8.9
5.0% 4.9 7.2
5.0% 5.4 7.4
5.0% 7.5 9.1
5.0% 5.7 7.4
5.0% 6.8 8.4
5.0% 6.4 8.1
5.0% 7.2 9.1
5.0% 4.9 6.9
5.0% 5.6 7.4
7.5% 5.6 7.0
7.5% 5 6.5
7.5% 3.8 5.1
7.5% 4.9 5.8
7.5% 6.9 7.9
7.5% 6.2 7.6
7.5% 5.5 6.6
7.5% 5.8 7.1
7.5% 6.2 7.6
7.5% 5.3 6.6
;
proc GLM;
class x percent;
model y=x percent;
means percent/LSD Duncan Dunnett;
run;
quit;

PROC  GLM；
CLASS percent；
MODEL y=percent  x / SOLUTION；
MEANS  percent / DUNCAN；
LSMEANS percent / STDERR PDIFF TDIFF；
RUN；