(x+3)+(x+3-6)+x=21

Solution for (x+3)+(x+3-6)+x=21 equation:

Simplifying
(x + 3) + (x + 3 + -6) + x = 21

Reorder the terms:
(3 + x) + (x + 3 + -6) + x = 21

Remove parenthesis around (3 + x)
3 + x + (x + 3 + -6) + x = 21

Reorder the terms:
3 + x + (3 + -6 + x) + x = 21

Combine like terms: 3 + -6 = -3
3 + x + (-3 + x) + x = 21

Remove parenthesis around (-3 + x)
3 + x + -3 + x + x = 21

Reorder the terms:
3 + -3 + x + x + x = 21

Combine like terms: 3 + -3 = 0
0 + x + x + x = 21
x + x + x = 21

Combine like terms: x + x = 2x
2x + x = 21

Combine like terms: 2x + x = 3x
3x = 21

Solving
3x = 21

Solving for variable 'x'.

Move all terms containing x to the left, all other terms to the right.

Divide each side by '3'.
x = 7

Simplifying
x = 7