What is the total number of students impacted by the projects with a donation from a donor with zip code "22205"?
zip code "22205" refers to donor_zip = '22205'; students impacted refers to students_reached
SELECT SUM(T2.students_reached) FROM donations AS T1 INNER JOIN projects AS T2 ON T1.projectid = T2.projectid WHERE T1.donor_zip = 22205