detaille les etape du calcul A= (3/4+7/4)x(7/12-1/3)  B= 4/5 x 2/9 + 2/3 x 1/3

A = (3/4 + 7/4) x (7/12 - 1/3) 
A = (10/4) x (7/12 - 1 x 4 / 3 x 4)
A = 10/4 x (7/12 - 4/12)
A = 10/4 x 3/12
A = 30/48
A = 6 x  5 / 6 x 8
A = 5/8

B = 4/5 x 2/9 + 2/3 x 1/3
B = 8/45 + 2/9
B = 8/45 + 2 x 5 / 9 x 5
B = 8/45 + 10/45
B = 18/45
B = 9 x 2 / 9 x 5
B = 2/5

A= (0,75+1,75) x (0,58-0,33)
A= 2,5 x 0,25
A= 0,625