A = 25/21 x 14/15
A = 350/315
A = 10/9
B =21/-6 x -9/56
B = 7/-2 x -9/56
B = -63/-112
B = -9/-16
C = -49/63 x -9/-28 (je pense que c'est -49, tu as écrit 49-)
C = -7/9 x -9/-28
C = 63/-252
C = 7/-28
C = 1/-4
D = 18/15 x 75/-16
D = 6/5 x 75/-16
D = 450/-80
D = -90/16
D = -45/8