I need to make a questionnaire to evaluate engineering department work (strengths and weaknesses) within the whole oil company.

when it comes for the population, organization has 550 employees. The department it self has 60 employees.

my question is: what is the number of respondents (from both organization and department) for questionnaire I need to have accepted number of sample sizes

( I need the source for your answer as well if possible)

Thanks in advance