Answer
Slump: $µ_{5}=µ_{4}\neµ_{3.75}$
Mixture: $µ_{67-0-301}=µ_{67-0-353}\neµ_{67-0-400}$
Work Step by Step
With the results from item (c) still available:
Select Stat -> ANOVA -> General Linear Model -> Comparisons
In Response select 28-day strength (psi). In Type of comparison select Pairwise. In Method select Tukey. In Choose terms for comparisons select Slump and Mixture.
Click OK.
