3a+9=21

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Solution for 3a+9=21 equation: 


Simplifying
3a + 9 = 21

Reorder the terms:
9 + 3a = 21

Solving
9 + 3a = 21

Solving for variable 'a'.

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

Add '-9' to each side of the equation.
9 + -9 + 3a = 21 + -9

Combine like terms: 9 + -9 = 0
0 + 3a = 21 + -9
3a = 21 + -9

Combine like terms: 21 + -9 = 12
3a = 12

Divide each side by '3'.
a = 4

Simplifying
a = 4

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