Hello, I'm working on Random Binomial Distributions and I was wondering how to solve this problem as it's the only one I can't figure out because of the wording. How do I find the amount of students who have already given blood in this survey?

"Of all college students who are eligible to give blood, about 18% do so on a regular basis. Each month a local blood bank sends an appeal to give blood to 250 randomly selected students. Find the average number of appeals in such mailings that are made to students who already give blood."