J'ai besoin d'aide pour l'exercice 51 svp ces urgent

A = 2/3 + 5/3 x 4/7
A = 2/3 + 20/21
A = 2 x 7 / 3 x 7 + 20/21
A = 14/21 + 20/21
A = 34/21

B = 1/5 + 7/5 x 2/3
B = 1/5 + 14/15
B = 1 x 3 / 5 x 3 + 14/15
B = 3/15 + 14/15
B = 17/15

C = 7/30 - 4/3 : 5/2
C = 7/30 - 4/3 x 2/5
C = 7/30 - 8/15
C = 7/30 - 8 x 2 / 15 x 2
C = 7/30 - 16/30
C = - 9/30
C = 3 x - 3 / 3 x 10
C = - 3/10

D = (4 - 1/3) + 5/4
D = (4 x 3 / 1 x 3 - 1/3) + 5/4
D = (12/3 - 1/3) + 5/4
D = 11/3 + 5/4
D = 11 x 4 / 3 x 4 + 5 x 3 / 4 x 3
D = 44/12 + 15/12
D = 59/12