BONJOURS J ai 2 exercice que je ne comprend merci de bien vouloir maider

Bonjour

Exercice I

x - 6 = 2
x = 2 +6
x = 8

x/2 -4 = 9
tu mets sous dénominateur 2
x - 8 = 18
x = 18 +8
x = 26/2
x = 13


3x +4 = 2x +7
3x -2x = 7 -4
x = 3

x/2 + 4 = x/6 +5
tu mets sous 12
6x + 48 = 2x + 60
6x - 2x = 60 -48
4x = 12
x = 3

Exercice II
A = (x+3)(4+x)
A = 4x +x² + 12 + 3x = x² + 7x +12

B = (5u +1)( 2 -3u)
B = 10u - 15u² +2 - 3u = -15u² +7u +2

C = (4z +3)²
C = 16z² + 24z +9