A random sample of 81 automobiles traveling on a section of an interstate showed an average speed of 60 mph. The distribution of speeds of all cars on this section of highway is normally distributed, with a standard deviation of 13.5 mph.

1. If we are interested in determining an interval estimate for ? at 86.9% confidence, the z value to use is

a. 1.96
b. 1.31
c. 1.51
d. 2.00

2. The value to use for the standard error of the mean is

a. 13.5
b. 9
c. 2.26
d. 1.5