Sample Size Calculation (HELP!)

Hi all,

I wish someone could help me out.

I am trying to estimate the sample size for a national health survey.

From the previous report, the prevalence rates of dental caries and gum diseases are 90% and 85%, respectively. What is the sample size if we are assuming a margin of error of 3% and 95% CI? Also, would the sample size be different if it's a one-sided or two-sided test?

I came across the online calculator; however, I am not sure if they are one-sided or two-sided.

We also have a mean DMFT score of 8.1 with a standard deviation of 7.1 for dental caries. Can I do the calculation by using n =(t X s / E)^2 if I assume the margin of error of 1 unit?

N=(1.96 X 7.1 / 1 ) ^ 2

Thank you for all your help =)