How many donors have endowment for the school named Glenn?
SELECT count ( DISTINCT T1.donator_name )  FROM endowment AS T1 JOIN school AS T2 ON T1.school_id   =   T2.school_id WHERE T2.school_name   =   "Glenn"
counting donors = COUNT(DISTINCT donor_name); endowment for school = JOIN on school_id; school named Glenn refers to school_name = 'Glenn'