Help with normal distribution problem

Don't know how my friend got the z1=-1.28, z2=1.28. Everything else is clear

The question:

The average salary of a male full professor at a public four-year institution offering classes at the doctoral level is $99,685. For a female full professor at the same kind of institution, the salary is $90,330. If the standard deviation for the salaries of both genders is approximately $5200 and the salaries are normally distributed, find the 80th percentile salary for the male professors and female professors.

Re: Help with normal distribution problem

i also do not understand how you got the two z scores. and the answers that were on that persons sheet were wrong to find the 80th percentile you can just go to the TABLE E chart and find the z score that corresponds to .8 which is .7995 which is under .84 so you then times .84(5200)+99685 to get 104,053 and do the same for the female. i am just confused on how you got -1.28 and 1.28