2x - 6 = 18
2x = 18 + 6 (24)
2x = 24
x = 12
3x + 9 = 2x + 24
3x + 9 = 2x + 24 - 9 (2x + 15)
3x = 2x + 15
3x - 2x = 15
x = 15
4x = 2.4? 0.4x = 2.4? I can't tell what the question is. Let me know in the comments and I'll answer it.
5x + 4 = 24
5x = 24 - 4 (20)
5x = 20
x = 4
2x / 3 = 4
2x = 4 * 3 (12)
x = 6
3(x + 7) = 51
3x + 21 = 51
3x = 51 - 21 (30)
3x = 30
x = 10
Hope I helped :)
