CREATE TRIGGER [dbo].[Joe_trigger] ON [dbo].[TableA]
    AFTER INSERT, UPDATE
AS
    BEGIN;
        UPDATE  B
        SET     LAST_MODIFIED = I.LAST_MODIFIED
        FROM    INSERTED AS I
                INNER JOIN TABLEB AS B
                    ON I.MATTER_UNO = B.MATTER_UNO
        WHERE   I.payor_Type = 'C';
    END;

CREATE TRIGGER [dbo].[Joe_trigger] ON [dbo].[TableA]
    AFTER INSERT, UPDATE
AS
    BEGIN;
        MERGE INTO TableB AS Tgt
            USING 
                (SELECT LAST_MODIFIED,
                        MATTER_UNO
                 FROM   INSERTED
                 WHERE  payor_Type = 'C') AS Src
            ON Tgt.MATTER_UNO = Src.MATTER_UNO
            WHEN MATCHED 
                THEN UPDATE
                    SET     LAST_MODIFIED = Src.LAST_MODIFIED;
    END;