The Infrastructure Report Card (IRC) reports that of 614,387 U.S. bridges, 9.1% were structurally deficient as of last year. The IRC also reports that more than 1300 California bridges fall under this category. How does California compare to the nation? Consider a random sample of 8749 bridges in California that includes 490 structurally deficient bridges. 

a. What is the sample proportion of structurally deficient bridges in California? 

b. Using 90% confidence, what is the margin of error? 

c. Using the results from parts (a) and (b), develop the 90% confidence interval estimate of the proportion of structurally deficient bridges in California. 

d. What does the confidence interval in part (c) lead you to conclude about California bridges?