The distribution of heights of American women aged 18 to 24

The distribution of heights of American women aged 18 to 24 is approximately normally distributed with mean 65.5 inches and standard deviation 2.5 inches. Approximately what percentage of women are between 60.5 and 68 inches tall? Use the empirical Rule.
a.) 0.34
b.)0.68
c.)0.815 .....i know 0.815 is the correct answer, but i dont know..HOW???
d.)0.95

Solution

Mean = 65.5
SD=2.5

z1 = (60.5-65.5)/2.5 = -2
z2 = (68-65.5)/2.5 = 1

P(60.5 < x < 68) = P(z2) - P (z1) = 0.8413 - 0.0228 = 0.8185 Answer (c)