The roster form of a set is the elements listed inside brackets { }.
In this case it is easy to visualize A - B directly of the Venn diagram: when you subtract from A those elements that are also in B, the result is A - B = {4, 11, 14}.
Now take into account tha (A - B)' is the complement of (A - B), this is all the elements that are not in A - B.
Being A - B = {4, 11, 14} then to show (A - B)' you just have to list all the elements that are on the figure except 4, 11 and 14.
The result, in roster form, is (A - B)' = {1, 2, 3, 5, 6, 7, 8, 9, 10, 12, 13}
A test statistic is calculated to compare with the critical value approach. The critical value is found by choosing any value of significance level ∝ = 0.05, 0.1 or 0.01 . Mostly 5% is preffered .
The the calculated value of the test statistic is compared with the chosen value rejection region that whether it falls in the critical region or not.
The test statistic is applied on the conditions given. For example comapring many results can be done by using chi square or comparing two means can be done by t test or testing the variation can be done by F - test.