How many purchases were made at Sac State American River Courtyard using Master Card?
Sac State American River Courtyard refers to LocationName = 'Sac State American River Courtyard'; Master Card refers to CreditCardType = 'MasterCard';
SELECT COUNT(T1.TransactionID) FROM `transaction` AS T1 INNER JOIN location AS T2 ON T1.LocationID = T2.LocationID WHERE T2.LocationName = 'Sac State American River Courtyard' AND T1.CreditCardType = 'MasterCard'