Does question 20 give the standard deviation for the private school students? I only see the mean given. In order to find the test statistic "Zobt" you usually need the mean and standard deviation of both of the populations, that being from private school and public school. The questions looks as though it is trying to compare social skill performance amongst TWO POPULATIONS. Also, you mentioned alpha is equal to .0 what? .05 .025 etc.?