Aidez-moi svp .... 3éme

bonjour

A = 3/4 + 5/4 : (4/3 - 1/2)
A = 3/4 + 5/4 : ( 8/6 - 3/6)
A = 3/4 + 5/4 : 5/6
A = 3/4 + 5/4 x 6/5
A = 3/4 + 30/20
a = 15/20 + 30/20
A = 45/20 = 9/4

B = 21 x 500 x 10⁻⁴ x 10 ⁶ sur 0.7 x 10 ⁸
B = 10 500 x 10 ² sur 0.7 x 10⁸
B = 15 000 x 10 ⁻⁶
B = 0.015
B = 1 .5 x 10 ⁻²

A = 7/15 - 2/15 x 9/4
A = 7/15 - 18/ 60
a = 28/60 - 18/60
A = 10/60 = 1/6

B = 25 x 3 x 10 ⁴ sur 2 x 10²
B = 75 x 10⁴ sur 2 x 10 ²
B = 37.5 x 10 ²
B = 3.75 x 10 ⁴
B = 37500