Bonjour,

a)

x = 4/3 +5/4

x= 16/12 + 15/12 = 31/12

b)

x=  5/7 -7/3

x=  15/21 - 49/21 = -34/21

c)

x= 3/12 +5/8

x = 6/24 +15/24

x= 21/24 = 7/8

d)

1/3 +2/9 = x

x =3/9 +2/9 = 5/9

e)

5/18 -11/45 = x

x= 25/90 - 22/90

x = 3/90 = 1/30

f)

x= -11/15 +12/25

x=  -55/75 + 36/75

x= -19/75

a) 31/12 ; b) -34/21 ; c) 7/8 ; d) -5/9 ; e) -1/30 ; f) -19/75