c+(c-1)+2(c-1)=21

Solution for c+(c-1)+2(c-1)=21 equation:

Simplifying
c + (c + -1) + 2(c + -1) = 21

Reorder the terms:
c + (-1 + c) + 2(c + -1) = 21

Remove parenthesis around (-1 + c)
c + -1 + c + 2(c + -1) = 21

Reorder the terms:
c + -1 + c + 2(-1 + c) = 21
c + -1 + c + (-1 * 2 + c * 2) = 21
c + -1 + c + (-2 + 2c) = 21

Reorder the terms:
-1 + -2 + c + c + 2c = 21

Combine like terms: -1 + -2 = -3
-3 + c + c + 2c = 21

Combine like terms: c + c = 2c
-3 + 2c + 2c = 21

Combine like terms: 2c + 2c = 4c
-3 + 4c = 21

Solving
-3 + 4c = 21

Solving for variable 'c'.

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

Add '3' to each side of the equation.
-3 + 3 + 4c = 21 + 3

Combine like terms: -3 + 3 = 0
0 + 4c = 21 + 3
4c = 21 + 3

Combine like terms: 21 + 3 = 24
4c = 24

Divide each side by '4'.
c = 6

Simplifying
c = 6