x + 13 = 20
x = 20 - 13
x = 7
-9 + x = 12
x = 12 + 9
x = 21
2x + 9 = 15
2x = 15 - 9
2x = 6 /:2
x = 3
[tex]\frac{1}{3}y - 3 = 7[/tex] /*3
y - 9 = 21
y = 21 + 9
y = 30
7x - 2 = 26
7x = 26 + 2
7x = 28 /:7
x = 4
4x - 6 = 30
4x = 30 + 6
4x = 36 /:4
x = 9
[tex]\frac{1}{5}x - 2 = 4[/tex] /*5
x - 10 = 20
x = 20 + 10
x = 30
y - 3 + y = 5
2y - 3 = 5
2y = 5 + 3
2y = 8 /:2
y = 4
5x - 4x + 1 = 2
x + 1 = 2
x = 2 - 1
x = 1
[tex]\frac{1}{2}x + 1 - x = -4[/tex] /*2
x + 2 - 2x = -8
-x + 2 = -8
- x = -8 - 2
-x = -10
x = 10
