Bonjour,

A)

7/3 *8 = 56/3

(56/3)/21 = 56 /(21*3) =56/63 =8/9

2/3 - 8/9 = 6/9 -8/9  = -2/9

B)

3/4 -5/6 = 9/12 -10/12 = -1/12

-1/12 *3 = -3/12 = -1/4

(-1/4) /2 = -1/8

C )

24/15 +35/25 =

24/15  +7/5 =  24/15 +21/15 = 45/15 = 3

3*20 = 60

60/33 = 20/11

D)

5/6 - 5/4 =  10/12 - 15/12 = -5/12

1/2 +2/3 = 3/6 +4/6= 7/6

(-5/12 )/(7/6)

(-5 *6) / (12*7) = -30/ 84  = -15/40 = -3/8