having trouble with hypotheses and finding value of test statistics

According to a report done by S & J Power, the mean lifetime of the light bulbs it manufactures is 43 months. A researcher for a consumer advocate group tests this by selecting 20 bulbs at random. For the bulbs in the sample, the mean lifetime is 45 months. It is known that the population standard deviation of the lifetimes is 7 months. Assume that the population is normally distributed. Can we conclude, at the 0.01 level of significance, that the population mean lifetime, H, of light bulbs made by this manufacturer differs from 43 months? Perform a two-tailed test. Then complete the parts below. Carry your intermediate computations to three or more decimal places, and round your responses as specified below. (If necessary, consult a list of formulas.) (a) State the null hypothesis Ho and the alternative hypothesis H