A university aacepts only applicats scoring in the top 16% on an entrance exam. Each year the test scores are normaly distributed with a standard deviation of 30. What is the highest value that the mean can have for Fred to be accepted with a score of 520?

I was able to figure out the answer to this question but now I can't seem to figure out how I got the z-score number of -0.99????

z=-0.99

x=520

o=30

mean= x+ (z+o)

= 520+(-0.99 x 30)

=490.3

ahh, help.