Suppose that the talk time on the Apple iPhone is approximately normally distributed with mean 9 hours and standard deviation 1.2 hour. (a) What proportion of the time will a fully charged iPhone last at least 6 hours? (b) What is the probability a fully charged iPhone will last less than 5 hours? (c) What talk time would represent the cutoff for the top 5% of all talk times? (d) Would it be unusual for the phone to last more than 11.5 hours? Why?

Can you use TI-84 to complete it?

I am having trouble how to find P(Z= a number) on the calculator.