1) Distribute on the left side of the equation:
3x - 21 - 6x = -x
Combine like terms:
-3x - 21 = -x
Add 3x to both sides:
-21 = 2x -x
Simplify:
-21 = x

2) Distribute on the left side of the equation:
5x + 20 + x = 6
Combine like terms:
6x + 20 = 6
Subtract 20 from both sides:
6x = -14
Divide by 6:
x = -14/6
x = -7/3

3) Distribute on the left side of the equation:
7 - 2x - 3 = 9
Combine like terms:
4 - 2x = 9
Subtract 4 from both sides:
-2x = 5
Divide by -2:
x = -5/2

Therefore, the solutions are x = -21, x = -7/3, and x = -5/2.