level of significance

Hi, googled stats help and found this great site. I'm a 42 year old guy who recently decided to back to grad school and the first class I dove into was statistics...maybe not the wisest decision but here we are. Having a homework issue right now. Here is the question:

During the past two years the vending machine in the building has charged $1.25 for a 20oz bottle of soda/water. During this time, records indicate that an average of 185 bottles were sold each week. The distribution of sales is approximately normal with a sd of 23. Recently, the prices have been increased to $1.50 per bottle. The weekly sales for the first 8 weeks after the increase are as follows: 148, 135, 142, 181, 164, 159, 192, 173. Do these data points indicate that there was a significant change in sales after the increase? Test at the .05 significance level.

- I know that since we know the sd we use a t distribution. I am not sure what my hypothesis should read but am I right in setting up the test statistic as follows:
z= xbar - mew
sd/square root of sample
The null hypothesis is H0 : Mu =185 Ha : Mu # 185
Sample t =Modulus ( (X bar -Mu)/( s.d./sqrt n) ).
Reject H0 if sample t >or= Table t with 7 degrees of freedom