Bonjour
A = (4/5 - 1/15) x (1/6 + 1/4)
A = [(4 x 3) / (5 x 3) - 1/15] x [(1 x 2) / (6 x 2) + (1 x 3) / (4 x 3)]
A = (12/15 - 1/15) x (2/12 + 3/12)
A = 11/15 x 5/12
A = 55/180
A = (5 x 11) / (5 x 36)
A = 11/36
B = 4/3 x (1/8 - 1)
B = 4/3 x [1/8 - (1 x 8) / (1 x 8)]
B = 4/3 x (1/8 - 8/8)
B = 4/3 x (- 7/8)
B = - 28/24
B = (4 x - 7) / (4 x 6)
B = - 7/6
C = (- 9/4 x 5/9) : (1 - 7/12)
C = - 45/36 : [(1 x 12) / (1 x 12) - 7/12]
C = - 45/36 : (12/12 - 7/12)
C = - 45/36 : 5/12
C = - 45/36 x 12/5
C = - 540/180
C = (180 x - 3) / (180 x 1)
C = - 3.