le 91, je n'arrive pas les fractions

Bonjour

A = (3/8 +1/4) + (4/3 - 1/6)
A = (3/8 + 2/8) +  ( 8/6 -1/6)
A = 5/8 + 7/6 = 20/24 + 28/24 = 48/24 = 2

B = 3/8 +1/4 +4/3 -1/6
B = 9/24 + 6/24 + 32/24 - 4/24 = 43/24

C = (3 +3/5 -7/12) x (1/4 - 2/5)
C = (180/60 + 36/60 - 35/60) x( 5/20 -8/20)
C = 181/60 x -3/20 = -543 /1200 = -181/400

D = (1/2 +1/3) : (3/4 -1/2 +1/3)
D = (3/6 +2/6) : (9/12 -6/12 +4/12)
D = 5/6 : 7/12
D = 5/6 x 12/7 = 60/42 = 10/7

E = -4/31 x [(2/3 +11/6) - (3/12 -1/3)]
E = -4/31 x [(4/6 +11/6) - (3/12 - 4/12)]
E = -4/31 x (15/6 +1/12)
E = -4/31 x (30/12 +1/12)
E = -4/31 x 31/12 = - 124/372 = -1/124

les / sont le traits de fraction
a= (3/8 + 1/4) + (4/3 - 1/6)
     (3/8 + 2/8) + (8/6 - 1/6)
     5/8 + 7/6
     30/48 + 56/48
     86/48
donc 43/24

b= 3/8 + 1/4 + 4/3 + 1/6
     9/24 + 6/24 + 32/24 - 4/24
donc 43/24

c= (3 + 3/5 - 7/12) x (1/4 - 2/5)
     (180/60 + 24/60 - 35/60) x (5/20 - 8/20)
     169/60 x -3/20
     -507/1200
     -169/400 

d= 1/2 + 2/3 / 3/4 - 1/12 + 1/3
     3/6 + 4/6 / 12/12 - 1/12 + 4/12
     7/6 / 15/12
     7/6 x 12/15
     84/90 
     14/15

e= -4/31 x [(2/3 + 11/6) - (3/12 - 1/3)]
     -4/31 x [(4/6 + 11/6) - (3/12 - 4/12)]
     -4/31 x (15/6 + 1/12)
     -4/31 x (30/12 + 1/12)
     -4/31 x 31/12
     -124/372
     -1/3