Quel est le résultat de ces opération stv

Bonjour,

A = 3/4 - 5/4 x 2/15
A = 3/4 - 10/60
A = (3 x 15) / (4 x 15) - 10/60
A = 45/60 - 10/60
A = 35/60
A = (5 x 7) / (5 x 12)
A = 7/12

B = 2 - 14/5 : 21/25 + 1/2
B = 2 - 14/5 x 25/21 + 1/2
B = 2 - 350/105 + 1/2
B = 1 - (35 x 10) / (35 x 3) + 1/2
B = 1 - 10/3 + 1/2
B = (1 x 6) / (1 x 6) - (10 x 2) / (3 x 2) + (1 x 3) / (2 x 3)
B = 6/6 - 20/6 + 3/6
B = 9/6 - 20/6
B = - 11/6