Bonjour
B= -9/7 - (3+2/21)
B = (- 9 x 3) / (7 x 3) - [(3 x 21) / (1 x 21) + 2/21]
B = - 27/21 - (63/21 + 2/21)
B = - 27/21 - 65/21
B = - 92/21
-1/15+3/2O
= (- 1 x 4) / (15 x 4) + (3 x 3) / (20 x 3)
= - 4/60 + 9/60
= 5/60
= (5 x 1) / (5 x 12)
= 1/12.