People were polled on how many books they read the previous year. Initial survey results indicate that s = 13.7 books. Complete parts (a) through (d) below. Click the icon to view a partial table of critical values. . . . . . (a) How many subjects are needed to estimate the mean number of books read the previous year within six books with 90% confidence? This 90% confidence level requires 15 subjects. (Round up to the nearest subject.) (b) How many subjects are needed to estimate the mean number of books read the previous year within three books with 90% confidence? This 90% confidence level requires 57 subjects. (Round up to the nearest subject.) (c) What effect does doubling the required accuracy have on the sample size? O A. Doubling the required accuracy nearly halves the sample size. O B. Doubling the required accuracy nearly quarters the sample size. O C. Doubling the required accuracy nearly doubles the sample size. D. Doubling the required accuracy nearly quadruples the sample size. (d) How many subjects are needed to estimate the mean number of books read the previous year within six books with 99% confidence? This 99% confidence level requires subjects. (Round up to the nearest subject.)