How many sales orders did the salesperson David R. Campbell create?
SP is an abbreviation for Sales Person; PersonType = 'SP';
SELECT COUNT(T2.TotalDue) FROM Person AS T1 INNER JOIN SalesOrderHeader AS T2 ON T1.ModifiedDate = T2.DueDate WHERE T1.FirstName = 'David' AND T1.MiddleName = 'R' AND T1.LastName = 'Campbell' AND T1.PersonType = 'SP'