Statistic ~ Find the critical value A manufacturer makes ball bearings that are supposed to have a mean weight of 30g. A retailer suspects that the mean weight is actually less than 30g. The mean weight for a random sample of 16 ball bearings is 28.6g with a standard deviation of 4.4g. At the 0.05 significance level, test the claim that the sample comes from a population with a mean weight less than 30g.

I did df = n - 1 = 16 - 1 = 15
invT (1 - 0.05, 15) = 1.753 but is wrong
What's the answer?