Question: From the total amount of donation to projects, what is the percentage of the amount is for school projects located in the rural area?
SQL: SELECT CAST(SUM(CASE WHEN T2.school_metro = 'rural' THEN T1.donation_to_project ELSE 0 END) AS REAL) * 100 / SUM(donation_to_project) FROM donations AS T1 INNER JOIN projects AS T2 ON T1.projectid = T2.projectid