I'm having trouble with finding relative frequency using 68-95-99.7 rule.

This is the question:

Assume the resting heart rates for a sample of individuals are normally distributed with a mean of

65 and a standard deviation of 20

Use the 68-95-99.7 rule to find the following quantities:

a. The relative frequency of rates less than 105 using the 68-95-99.7 rule is ____

(Round to three decimal places as needed.)

b. The relative frequency of rates greater than 85 using the 68-95-99.7 rule is ____

(Round to three decimal places as needed.)

c. The relative frequency of rates between 25 and 65 using the 68-95-99.7 rule is ____

(Round to three decimal places as needed.)