r+9=21

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Solution for r+9=21 equation: 


Simplifying
r + 9 = 21

Reorder the terms:
9 + r = 21

Solving
9 + r = 21

Solving for variable 'r'.

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

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

Combine like terms: 9 + -9 = 0
0 + r = 21 + -9
r = 21 + -9

Combine like terms: 21 + -9 = 12
r = 12

Simplifying
r = 12

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