Determine sample size for unknown population?

https://www.statisticshowto.datasciencecentral.com/probability-and-statistics/find-sample-size/#CI1

Thank you so much for your reply!

Just because the number of women, the number of people with disability, and the number of people with mental health problems are all large, the number of women with disability and mental health problems should also be large. So, a simple guess is just the multiplicative product of three proportions, say (.5)(.05)(.05) = .00125. If the overall adult population is 5 million, then the target population will be 6,250.