Hey tjang.

Hint: If you are getting the distribution of the mean then the variance of the estimator is Sample_Variance/#Number of observations in sample.

In other words (x_bar - mu)/[Sample_Variance/Number_Of_observations] ~ t_(n-1) = t distribution with (n-1) degrees of freedom.

You can then re-arrange to get the distribution of mu and test the hypothesis mu > 255 if your variables correspond to daily spending.