Donner chaque calcul sous la forme d'une fraction irréductible. Merci pour votre aide !

A = 2/7 - 15/7 : 5/4
A = 2/7 - 15/7 x 4/5
A = 2/7 - 60/35
A = 2 x 5 / 7 x 5 - 60/35
A = 10/35 - 60/35
A = 50/35
A = 5 x 10 / 5 x 7
A = 10/7

B = 11/8 + 7/18 x 2/7
B = 11/8 + 14/126
B = 11 x 126 / 8 x 126 + 14 x 8 / 126 x 8
B = 1386/1008 + 112/1008
B = 1498/1008
B = 14 x 107 / 14 x 72
B = 107/72

C = 5/6 + 5/6 x 7/9
C = 5/6 + 35/54
C = 5 x 9 / 6 x 9 + 35/54
C = 45/54 + 35/54
C = 80/54
C = 2 x 40 / 2 x 27
C = 40/27