Bonjour
A = 4/8 - 32/20
A = (4 x 5) / (8 x 5) - (32 x 2) / (20 x 2)
A = 20/40 - 64/40
A = - 44/40
A = (4 x - 11) / (4 x 10)
A = - 11/10
B = 3/10 + - 3/4
B = (3 x 2) / (10 x 2) - (3 x 5) / (4 x 5)
B = 6/20 - 15/20
B = - 9/20
C = (- 9/16 - 2/3) + 5/4
C = [(- 9 x 3) / (16 x 3) - (2 x 16) / (3 x 16)] + (5 x 12) / (4 x 12)
C = (- 27/48 - 32/48) + 60/48
C = - 59/48 + 60/48
C = 1/48.