8-4=

4

24-12=

12

14-7=

7

20-10=

10

2-1=

1

22-11=

11

4-2

2

12-6=

6

18-9

9

6-3=

3

10-5

5

16-8=

8

                                     12

                                     -6

                                  _____

6

                                      24

                                     -12

                                   _____

12

                                       4

                                      -2

                                     ___

2

                                    18

                                  -  9

                                   ___

9

                                      10

                                     - 5

                                     ___

5

                                   8

                                  -4

                               _____

4

                                     14

                                     -7

                                  _____

7