From the same survey as in Exercise 9, 294 of the 409 respondents who reported earning less than $30,000 per year said they were social networking users. At the other end of the income scale, 333 of the 504 respondents reporting earnings of $75,000 or more were social networking users.

a) Find the proportions of each income group who are social networking users.

b) What is the difference in proportions?

c) What is the standard error of the difference?

d) Find a 95% confidence interval for the difference between these proportions.