svp qui peut m aider urgent c tous les exo merci d avance

bonjour

A = 8/14 + 15/21
A = 24/42 + 30/42
A = 54/42 = 9/7

B = 7/9 - 14/63
B = 49/63 - 14/63
B = 35/63 = 5/9

C = 15/20 + 14/8
C = 30/40 + 70/40
C = 100/40 = 5/2


9/7 = 6/7 + 3/7
12/35 = 8/35 + 4/35
9/11 = 13/11 - 4/11

5/2 + 3/2 = 8/2
4/7 - 3/7 = 1/7
2/5 + 3/5 = 5/5 = 1