How many furniture products had been shipped by standard class in the East superstore?
furniture products refers to Category = 'Furniture'; shipped by standard class refers to "Ship Mode" = 'Standard Class'
SELECT COUNT(T2.Category) FROM east_superstore AS T1 INNER JOIN product AS T2 ON T1.`Product ID` = T2.`Product ID` WHERE T1.`Ship Mode` = 'Standard Class'