Answer
$µ_{87~Octane}=µ_{89~Octane}\neµ_{92~Octane}$
Work Step by Step
With the results from item (a) still available:
Select Stat -> ANOVA -> General Linear Model -> Comparisons
In Response select C3. In Type of comparison select Pairwise. In Method select Tukey. In Choose terms for comparisons select C2 (treatments).
Click OK.
