21-2a=9

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Solution for 21-2a=9 equation: 


Simplifying
21 + -2a = 9

Solving
21 + -2a = 9

Solving for variable 'a'.

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

Add '-21' to each side of the equation.
21 + -21 + -2a = 9 + -21

Combine like terms: 21 + -21 = 0
0 + -2a = 9 + -21
-2a = 9 + -21

Combine like terms: 9 + -21 = -12
-2a = -12

Divide each side by '-2'.
a = 6

Simplifying
a = 6

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