Aider moi svp exercice 7 !

3/4 = 6/8
6/8 - 7/8 = -1/8


3/10 = 15/60
7/12 = 35/60
15/60 - 35/60 = -1/3


4/9 - 5/12 = impossible


5/6 = 10/12
3/4 = 9/12
10/12 - 9/12 = 1/12


5/-9 - 18/-9 = 13/9
23/8 = 46/16
46/16-(-5/16) =51/16