How many employees in total are in charge of the sales in the Eastern Region?
Eastern Region refers to RegionDescription = 'Eastern';
SELECT COUNT(T.EmployeeID) FROM ( SELECT T3.EmployeeID FROM Region AS T1 INNER JOIN Territories AS T2 ON T1.RegionID = T2.RegionID INNER JOIN EmployeeTerritories AS T3 ON T2.TerritoryID = T3.TerritoryID WHERE T1.RegionDescription = 'Eastern' GROUP BY T3.EmployeeID ) T