Maths 14 stats and probability

A physical therapist wants to determine the difference in the proportion of men and women who participate in regular sustained physical activity. What sample size should be obtained if he wishes the estimate to be within five percentage points with 90% confidence, assuming that (a) he uses the estimates of 21.8% male and 18.4% female from a previous year? (b) he does not use any prior estimates? (a) n= (Round up to the nearest whole number.) (b) n= (Round up to the nearest whole number.)