B = 5/6 + 7/9 = 15/18 + 14/18 = 29/18
C = -21/8 x -24/49 = tu simplifies d'abord 8 et 24
C = -21/1 x -3/49 = 63/49 = 9/7
D = 2/9+5/3+15/4 = 24/108 + 180/108 + 405/108 = 609/108 = 203/36
E = (4/5-2) x 3/4-2/3) = (4/5 + 10/5) x ( 9/12 -8/12)
= 14/5 x 1/12 = 14/60 = 7/30