Answer:
16
Step-by-step explanation:
Remember that the general formula for SSTR is
[tex]SSTR = n_1(\bar{x_1}-\bar{x})+...+n_k(\bar{x_k}-\bar{x})[/tex]
For this problem
[tex]\bar{x} = 8[/tex]
[tex]n_1 = n_2 = n_3 = n_4 = 4[/tex]
then
[tex]n_1(\bar{x_1}-\bar{x})+...+n_k(\bar{x_k}-\bar{x}) = 32[/tex]
so once you have the SSTR then the MSTR is given by the following formula
[tex]MSTR = \frac{SSTR}{t-1}[/tex]
where [tex]t[/tex] is the number of treatments, for this case the number of treatments is 3 so [tex]t = 3[/tex] and
[tex]MSTR = \frac{32}{3-2} = \frac{32}{2} = 16[/tex]