Exo 48 aidez moi svp niveau 3ème simplifier plus que possible

a) 5/4
b) 2/9
c) 2/12
d)7/21

3/4 + 1/2 = 3/4 + 2/4 = 5/4

1/3 - 5/9 = 3/9 - 5/9 = -2/9

-7/12 + 3/4 = -7/12 + 9/12 = 2/12 = 1/6

4/7 - 5/21 = 12/21 - 5/21 = 7/21 = 1/3

-3/35 - 3/7 = -3/35 - 15/35 = -18/35

7/4 - (-5/28) = 7/4 + 5/28 = 49/28 - 5/28 = 44/28 = 11/7