A random sample of 500 adult residents of Maricopa County indicated that 385 were in favor of increasing the highway speed limit to 75 mph, and another sample of 400 adult residents of Pima County indicated that 267 were in favor of the increased speed limit.

(a) Do these data indicate that there is a difference in the support for increasing the speed limit for the residents of the two counties? Use α = 0.05. What is the P-value for this test?

(b) Construct a 95% confidence interval on the difference in the two proportions. Provide a practical interpretation of this interval.