Besoin d'aide pour ces 3 exercices svp c'est urgent !

exercice 20
a) 3x+7 = 34
3x = 34-7
3x = 27
x = 27/3
x = 9

b) 2+4y = -6
4y = -6-2
4y = -8
y = -8/4
y = -2

c) -3-2x = 7
-2x = 7+3
-2x = 10
x = -10/2
x = -5

d) -3 = -3t-12
-3+12 = -3t
9 = -3t
t = -9/3
t = -3

Exercice 21
a) -2x+7 = 12
-2x = 12-7
-2x = 5
x = -5/2

b)-2+3y = -6
3y = -6+2
3y = -4
y = -4/3

c) 5-2x = 12
-2x = 12-5
-2x = 7
x = -7/2

d) -1/2 = -3t/2 -5/2
-1/2+5/2 = -3t/2
4/2 = -3t/2
2*(4/2) = -3t
4 = -3t
t = -4/3

Exercice 22
a) 3x+7 = x+2
3x = x+2-7
3x-x = -5
2x = -5
x = -5/2

b) 2+2y = -1 +3y
2+2y +1 = 3y
3 = 3y -2y
3 = y
y = 3

c) 4-5a = 2a-1
4-5a+1 = 2a
5 = 2a+5a
5 = 7a
a = 5/7

d) t-4 = -3t-10
t-4+3t = -10
4t = -10-4
4t = -14
t = -14/4
t = -7/4