Aide urgente exercice de Math ( produit en croix) Merci! :)

bonsoir

z/5 = 3/4
4z = 15
z = 15/4

x/7 = -2/13
6x = 49 et x = 49/6

x/11 = - 2/13
13x = -22
x = -22/13

x/-8 = 8/9
9x = - 64
x = -64/9

-x/12 = 7/3
-3x = 84
x = - 84/3 = -28

7x/2 = 1/4
28x = 2
x = 2/28 = 1/14

2x/9 = -7/27
54x = - 63
x = - 63/54 = - 7/8

-3x/7 = 7/8
-24x = 49
x = - 49/24

-11x/9 = - 1/5
-55x = - 9
x = 9/55