HELP, I don't understand this

Question

The scores on a psychology exam were normally distributed with a mean of

63 and a standard deviation of 9.

A failing grade on the exam was anything 2 or more standard deviations below the mean. What was the cutoff for a failing​ score? Approximately what percentage of the students​ failed?

Answer 1

9*2=18 points less than the mean

63-18=45

Look up the z score table: It is 2.28%