Given that the population standard deviation = $275 for the expenses for the professional development activities by the employees of a LARGE company....

Given that the population standard deviation = $275 for the expenses for the professional development activities by the employees of a LARGE company. How large a sample must be taken to construct a confidence interval for the mean expenses for the professional development activities for all the employees with a margin of error of no more than $25.00

How do you determine the a 90% confidence with the given statement?