6-2(6+a)-a=-18

Solution for 6-2(6+a)-a=-18 equation:

Simplifying
6 + -2(6 + a) + -1a = -18
6 + (6 * -2 + a * -2) + -1a = -18
6 + (-12 + -2a) + -1a = -18

Combine like terms: 6 + -12 = -6
-6 + -2a + -1a = -18

Combine like terms: -2a + -1a = -3a
-6 + -3a = -18

Solving
-6 + -3a = -18

Solving for variable 'a'.

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

Add '6' to each side of the equation.
-6 + 6 + -3a = -18 + 6

Combine like terms: -6 + 6 = 0
0 + -3a = -18 + 6
-3a = -18 + 6

Combine like terms: -18 + 6 = -12
-3a = -12

Divide each side by '-3'.
a = 4

Simplifying
a = 4