SUBTRACTING THREE DIGIT NUMBERS-19a
                                                        BORROW 1 FROM 10'S
Example:   923  Simply the problem:                       
        -  899      thousands   hundreds    tens    ones       ONES
           ---      ---------   --------    ----    ----      -----
            24                     9         2       3   10 +3=  13 
                                   8         9       9            9
                                 ---       ---     ---         ----
                                                                  4

                                                        BORROW 1 FROM 100'S

                                             1           10 +1=  11
                                             9                    9
                                                               ----
                                   8                               2
                                   8
                                 ----       ---     ---
                                   0          2        4
END