svp l'exercice 80 a faire il faut justifier les étapes

A=(1-1/7):12/5
A=(1*7/1*7-1/7 ):12/5
A=(7/7-1/7):12/5
A=6/7:12/5
A=6/7*5/12
A=30/84
A=6*5/14*6
A=5/14

B=(1/4-1/5)*(7+37/9)
B=(1*5/4*5-1*4/5*4)*(7*9/1*9+37/9)
B=(5/20-4/20)*(63/9+37/9)
B=1/20*100/9
B=100/180
B=10*10/18*10
B=10/18
B=2*5/2*9
B=5/9

C=2/3+1/6:2-1/2
C=2*2/3*2+1/6:2*2/1*2-1/2
C=4/6-1/6:4/2-1/2
C=3/6:3/2
C=3/6*2/3
C=6/18
C=6*1/6*3
C=1/3

D=3/4+1/2*(2/3-1)
D=3/4+1/2*(2/3-1*3/1*3)
D=3/4+1/2*(2/3-3/3)
D=3/4+1/2*(-1)/3
D=3/4+(-1)/6
D=3*3/4*3+(-1)*2/6*2
D=9/12-2/12
D=7/12