Answer:
c. 81
Step-by-step explanation:
The number of ANOVA degrees of freedom is given by the following formula:
[tex]df = (n-1)*(k-1)[/tex]
In which n is the size of the sample and k is the number of events.
In this problem, we have that:
[tex]n = 28, k = 4[/tex]
So
[tex]df = (n-1)*(k-1)[/tex]
[tex]df = 27*3 = 81[/tex]
The correct answer is:
c. 81