For the within-treatments estimate of population variance, the MSE has a numerator and a denominator.
In words, describe the numerator. (Same objective as 2.a.)
In words, describe the denominator. (Same objective as 2.a.)
While the denominator of the MSTR is of course relevant, the key determinant of the MSE is the numerator. Why? (Hint: the answer lies in what the numerator is.)