URGEENT SVP : besoin d'aide pour l'exercice 34 merci

A = 15/14 - 6/7 x 2/3
A = 15/14 - 12/21
A = 15 x 3 / 14 x 3 - 12 x 2 / 21 x 2
A = 45/42 - 24/42
A = 21/42
A = 21 x 1 / 21 x 2
A = 1/2

B = 3/4 + 1/2 x (2/3 - 1)
B = 3/4 + 1/2 x (2/3 - 1 x 3 / 1 x 3)
B = 3/4 + 1/2 x (2/3 - 3/3)
B = 3/4 + 1/2 x (- 1/3)
B = 3/4 - 1/6
B = 3 x 6 / 4 x 6 - 1 x 4 / 6 x 4
B = 18/24 - 4/24
B = 14/24
B = 2 x 7 / 2 x 12
B = 7/12

C = 1/2 - 3/4 : 5/2
C = 1/2 - 3/4 x 2/5
C = 1/2 - 6/20
C = 1 x 10 / 2 x 10 - 6/20
C = 10/20 - 6/20
C = 4/20
C = 4 x 1 / 4 x 5
C = 1/5

D = 4/3 - 2/5
     5/2 + 3/10
D = 4 x 5 / 3 x 5 - 2 x 3 / 5 x 3
         5 x 5 / 2 x 5 + 3/10
D = 20/15 - 6/15
     25/10 + 3/10
D = 14/15 : 28/10
D = 14/15 x 10/28
D = 140/420
D = 140 x 1 / 140 x 3
D = 1/3