According to a report done by S & J Power, the mean lifetime of the light bulbs it manufactures is 55 months. A researcher for a consumer advocate group tests this by selecting 100 bulbs at random. For the bulbs in the sample, the mean lifetime is 57 months. It is known that the population standard deviation of the lifetimes is 8 months. Can we conclude, at the 0.10 level of significance, that the population mean lifetime, μ, of light bulbs made by this manufacturer differs from 55 months? Find the value of the test statistic. Find the two critical values.