Réponse:
B= 2/9 ÷ (1/4 -2/3)
B= 2/9 ÷ (3/12 -8/12)
B= 2/9 ÷ (-5/12)
B= 2/9 × -12/5
B= -24/45
B= -8/15
C= (3/7 + 1/2) ÷ 4/7
C= (6/14 + 7/14) ÷ 4/7
C= 13/14 ÷ 4/7
C= 13/14 × 7/4
C= 13/2 × 1/4
C= 13/8
