A fire department in a rural county reports that its response time to fires is approximately normally distributed with a mean of 22 minutes and a standard deviation of 3.9 minutes.

a. What proportion of all response times for this fire department are below 18.5 minutes?

b. What proportion of all response times for this fire department are above 23.2 minutes?

c. Use the 68-95-99.7 rule to find the proportion of response times between 14.2 and 29.8 minutes.