Write SQL query to solve given problem: What is the average total donations received by Fresno County colleges?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT SUM(T2.donation_optional_support + T2.donation_to_project) / COUNT(donationid) FROM projects AS T1 INNER JOIN donations AS T2 ON T1.projectid = T2.projectid WHERE T1.school_county = 'Fresno'