Production managers on an assembly line must monitor output to check the average weight (kilograms) of their product. If the average weight is less than 15 kilograms, the assembly line must be stopped, and the machinery serviced. They continuously inspect a random sample of production runs and find the average weight of a sample of products, to check that the manufacturing process is working correctly. The hypotheses are:

Ho: = 15

Ha: < 15

Say a random sample of 30 products is taken, where the mean weight is found to be 9.2 kilograms with a standard deviation of 0.2 kilograms.

If testing at the 1% level of significance, what is the critical value?