options nocenter nodate;

data a;
  input salinity days uptake;
  cards;
0 14 2.2
0 14 3.3
0 21 5.0
0 21 5.7
0 28 13.2
0 28 12.4
6 14 3.7
6 14 4.5
6 21 5.9
6 21 7.2
6 28 9.4
6 28 11.0
12 14 2.8
12 14 3.4
12 21 4.5
12 21 5.9
12 28 7.6
12 28 8.3
;

proc glm;
  class salinity days;
  model uptake=salinity days salinity*days;
run;

proc glm;
  model uptake=salinity salinity*salinity days days*days
               salinity*days salinity*days*days salinity*salinity*days
               salinity*salinity*days*days;
run;

proc glm;
  model uptake=salinity days days*days salinity*days salinity*days*days / solution clparm;
  estimate 'Intercept for day 14' intercept 1 days 14 days*days 196;
  estimate 'Intercept for day 21' intercept 1 days 21 days*days 441;
  estimate 'Intercept for day 28' intercept 1 days 28 days*days 784;
  estimate 'Slope for day 14' salinity 1 salinity*days 14 salinity*days*days 196;
  estimate 'Slope for day 21' salinity 1 salinity*days 21 salinity*days*days 441;
  estimate 'Slope for day 28' salinity 1 salinity*days 28 salinity*days*days 784;
  estimate 'Intercept for salinity 0' intercept 1 salinity 0;
  estimate 'Intercept for salinity 6' intercept 1 salinity 6;
  estimate 'Intercept for salinity 12' intercept 1 salinity 12;
  estimate 'Linear coefficient for salinity 0' days 1 salinity*days 0;
  estimate 'Linear coefficient for salinity 6' days 1 salinity*days 6;
  estimate 'Linear coefficient for salinity 12' days 1 salinity*days 12;
  estimate 'Quadratic coefficient for salinity 0' days*days 1 salinity*days*days 0;
  estimate 'Quadratic coefficient for salinity 6' days*days 1 salinity*days*days 6;
  estimate 'Quadratic coefficient for salinity 12' days*days 1 salinity*days*days 12;
  estimate 'Day 28 - Day 21 when salinity 6'
            days 7 days*days 343 salinity*days 42 salinity*days*days 2058;
  estimate 'Day 28 - Day 21 when salinity 12'
            days 7 days*days 343 salinity*days 84 salinity*days*days 4116;
run;