hw help

an instructor has been teaching large sections of business statistics for the past 10 semesters. As a group, final exam scores are normally distributed with mew = 42 and sd = 9. With the current class of n=100 students, the instructor tries a different format. He shows stand up comedy before class at at breaks. At the end of the semester, the instructor notes that the mean for this section on the final was xbar = 46.5. Did the teaching format have a significant effect on performance on the final exam? Test with alpha set at .05.

a) state the hypothesis
b) compute the test statistic
c) make a decision regarding Ho

Okay, trouble starting with the hypothesis. I think it should be Ho: = 42 vs Ha: not = 42. i am having trouble setting up the test statistic also....

i think it would read:
9/square root 100

am i heading in the right direction?