Bonjour,
A=-9/8*(-1/6-5/4)
A = - 9/8 x (1 x 2 / 6 x 2 - 5 x 3 / 4 x 3)
A = - 9/8 x (2/12 - 15/12)
A = - 9/8 x - 13/12
A = 117/96
A = 3 x 39 / 3 x 32
A = 39/32
B=7/9+-4/9÷1/4
B = 7/9 - 4/9 : 1/4
B = 7/9 - 4/9 x 4
B = 7/9 - 16
B = 7/9 - 16 x 9 / 1 x 6
B = 7/9 - 144/9
B = - 137/9