How to solve negative exponents with a negative base?

2people are trying different phones to see which one has the better talk time. chatlong has an average of 18 hours with a standard deviation of 2 hours and talk-a-lot has an average of 20 hours with a standard deviation of 3. the two people who tested their phones both got 20 hours of use on their phones. for the z-scores i got 1 for the chatlong company and 0 for talk-a-lot. what is the percentile for each z-score?

Layla answer 21 of the 25 questions on his history test correctly. what decimal represents the fraction of problem he answer incorrectly.

Ineed to find the answer to number 2