а-б:

8-(-13) = 8+13 = 21

0-(-7) = 7

-4-(-16) = -4+16 = 16-4 = 12

-15-4 = -19

1-15 = -14

-18-0 = -18

б-а:

-13-8=-21

-7-0 = -7

-16-(-4) = -16+4 = -12

4-(-15) = 4+15 = 19

15-1 = 14

0-(-18) = 0+18 = 18