What is the average donation amount to a project created by a teacher working in a school in Brooklyn?
school in Brooklyn refers to school_city = 'Brooklyn'; Average = AVG(donation_total);
SELECT SUM(T2.donation_total) / COUNT(donationid) FROM projects AS T1 INNER JOIN donations AS T2 ON T1.projectid = T2.projectid WHERE T1.school_city = 'Brooklyn'