please explain

Facebook: A study showed that two years ago, the mean time spent per visit to Facebook was 20.0 minutes. Assume the standard deviation is o = 8.0 minutes. Suppose that a simple random sample of 104 visits was selected this year and has a sample mean of x = 19.0 minutes. A social scientist is interested to know whether the mean time of Facebook visits has decreased. Use the a = 0.01 level of significance and the P-value method with the TI-84 calculator. (a) State the appropriate null and alternate hypotheses. (b) Compute the P-value. (c) State a conclusion. Use the a = 0.01 level of significance