A study on the proportion of consumers of celiac and vegetarian food established that, among the employees of a company, only between 20% and 35% respectively consumed this type of food.

a) What was the observed sample percentage?

b) If the study was carried out considering a sample of 40 collaborators, what margin of error was used?

c) If the analysis was carried out with a confidence level of 95%, how many collaborators made up the selected sample?