According to media research, the typical American listed to 195 hours of music in the last year. This is down from 290 hours four years earlier. Dick Trythall is a big country and western music fan. He listens to music while working around the house, reading, and riding in his truck. Assume the number of hours spent listening to music follows a normal probability distribution with a standard deviation of 8.5 hours.

a) If Dick is in the top 1 percent in terms of listening time, how many hours dose he listen per year?

b) Assume that the distribution of times four years earlier also follows the normal probability distribution with a standard deviation of 8.5 hours. How many hours did the 1 percent who listen to the least music acutally listen?

I already have the soultution to this question (attached in the file), but what i don't understand is how do i know that i have to use the formula used in a for a and the formula used in b for b. So I don't really understand the difference between a and b. Could anybody help me out with that. I hope it is not too confusing.