21=r-12

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Solution for 21=r-12 equation:


Simplifying
21 = r + -12

Reorder the terms:
21 = -12 + r

Solving
21 = -12 + r

Solving for variable 'r'.

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

Add '-1r' to each side of the equation.
21 + -1r = -12 + r + -1r

Combine like terms: r + -1r = 0
21 + -1r = -12 + 0
21 + -1r = -12

Add '-21' to each side of the equation.
21 + -21 + -1r = -12 + -21

Combine like terms: 21 + -21 = 0
0 + -1r = -12 + -21
-1r = -12 + -21

Combine like terms: -12 + -21 = -33
-1r = -33

Divide each side by '-1'.
r = 33

Simplifying
r = 33

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