How many total items were requested for the Onslow Co School District urban metro school projects?
Onslow Co School District refers to school_district = 'Onslow Co School District';
SELECT SUM(T1.item_quantity) FROM resources AS T1 INNER JOIN projects AS T2 ON T1.projectid = T2.projectid WHERE T2.school_metro = 'urban' AND T2.school_district = 'Onslow Co School District'