Pouvez vous m'aider pour le 34 svp

a) 4/15 + 16/15 = 19/15
b) 12/21 + 2/21 = 14/21 = 7 x 2 / 7 x 3 = 2/3
c) 31/9 + 5/9 = 36/9 = 9 x 4 / 9 x 1 = 4
d) 17/6 + 23/6 = 40/6 = 2 x 20 / 2 x 3 = 20/3