Quelqu'un peut m'aider c l'exercice 24 et merci

Bonjour,

A = - 13/6 + - 9/4
A = - 13/6 - 9/4
A = - 13 x 4 / 6 x 4 - 9 x 6 / 4 x 6
A = - 52/24 - 54/24
A = - 106/24
A = 2 x - 53 / 2 x 12
A = - 53/12

B = - 7/15 + 11/6
B = - 7 x 2 / 15 x 2 + 11 x 5 / 6 x 5
B = - 14/30 + 55/30
B = 41/30

C = 7/8 + - 11/6
C = 7/8 - 11/6
C = 7 x 3 / 8 x 3 - 11 x 4 / 6 x 4
C = 21/24 - 44/24
C = - 23/24