A random sample of 64 automobiles traveling on a section of an interstate showed an average speed of 65 mph. The distribution of speeds of all cars on this section of highway is normally distributed, with a standard deviation of 13.5 mph. If we are interested in determining an interval estimate for μ at 84.7% confidence, the z value to use is _____.
a. 1.43
b. 1.02
c. 1.96
d. 2.00