having a really hard time on this, had to miss two classes last week and now i have no idea what i'm doing. I checked my book but i think i'm missing something. can anyone help? step by step help is greatly appreciated

A producer of various kinds of batteries has been producing "D" size batteries with a life

expectancy of 87 hours. Due to an improved production process, management believes that there has

been an increase in the life expectancy of their "D" size batteries. A sample of 36 batteries showed an

average life of 88.5 hours. Assume from past information that it is known that the standard deviation of

the population is 9 hours.

a. Give the null and the alternative hypotheses.

b. Compute the standardized test statistic.

c. At 1% (α = .01) significance level test management's belief. State your conclusion