In each of the following cases, calculate a confidence interval to estimate p1 - p2.
a. n1 = 85, n2 = 90, p̂1 = .75, p̂2 = .67, level of confidence = 90%
b. n1 = 1100, n2 = 1300, p̂1 = .19, p̂2 = .17, level of confidence = 95%
c. n1 = 430, n2 = 399, x1 = 275, x2 = 275, level of confidence = 85%
d. n1 = 1500, n2 = 1500, x1 = 1050, x2 = 1100, level of confidence = 80%