Calculating sample size based on population proportion

With a 90% confidence interval, what size sample would we need based on the proportion of population in proportion to sample size?

Null hypothesis: There is a taste difference between the two brands so consumers will be able to identify the difference in brand seventy percent of the time. The alternate null hypothesis asserts that there is no distinct difference in taste between the types of brand, which is not recognizable more than 7/10 of the time.

This solution provides steps to calculate the sample size based on the population proportion.