Look at your bell curve one standard deviation above and one standard deviation below covers approx 68 %
54-13 = 41 54 + 13 = 67
so between 41 and 67 covers 68%
z score for 80 - z score for 28 =
80 is two SD 28 is - 2SD
.9772 - 0228 = .9544 = ~ ~ 95%