Mathématiques urgent !!! La 3ème fois que demande de l'aide depuis hier et personne ne me repond exercices 17-18 merci

17)
A = 24/5 x 3/8
A = 72/40
A = 8 x 9 / 8 x 5
A = 9/5

B = 9/21 x 14/11
B = 126/231
B = 21 x 6 / 21 x 11
B = 6/11

C = 30/8 x 5/12
C = 150/96
C = 6 x 25 / 6 x 16
C = 25/16

D = 4/27 x 81/4
D = 324/108
D = 108 x 3 / 108 x 1
D = 3

18)
A = 20/9 x 3/16
A = 60/144
A = 12 x 5 / 12 x 12
A = 5/12

B = 64/15 x 10/8
B = 640/120
B = 40 x 16 / 40 x 3
B = 16/3

C = 21/24 x 16/14
C = 336/336
C = 1

D = 6/15 x 35/14
D = 210/210
D = 1