Determine the overall sample size required so that a 99% confidence interval for the difference of two proportions will have a margin of error of ???????? = 0.04 when

(a) ????̇ ???? = 0.25 and ????̇ ???? = 0.20.

(b) ????̇ ???? = 0.40 and ????̇ ???? = 0.30.

(c) ????̇ ???? = 0.80 and ????̇ ???? = 0.90.

(d) no prior knowledge of the proportions is available.