Solve for r
r=9
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81=9r
Variable r cannot be equal to 0 since division by zero is not defined. Multiply both sides of the equation by r.
9r=81
Swap sides so that all variable terms are on the left hand side.
r=\frac{81}{9}
Divide both sides by 9.
r=9
Divide 81 by 9 to get 9.
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