12+9=x

Solution for 12+9=x equation:

Simplifying
12 + 9 = x

Combine like terms: 12 + 9 = 21
21 = x

Solving
21 = x

Solving for variable 'x'.

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

Add '-1x' to each side of the equation.
21 + -1x = x + -1x

Combine like terms: x + -1x = 0
21 + -1x = 0

Add '-21' to each side of the equation.
21 + -21 + -1x = 0 + -21

Combine like terms: 21 + -21 = 0
0 + -1x = 0 + -21
-1x = 0 + -21

Combine like terms: 0 + -21 = -21
-1x = -21

Divide each side by '-1'.
x = 21

Simplifying
x = 21