Solve for r
r=\frac{10x}{21}
Solve for x
x=\frac{21r}{10}
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\frac{10}{21}x=r
Combine \frac{1}{3}x and \frac{1}{7}x to get \frac{10}{21}x.
r=\frac{10}{21}x
Swap sides so that all variable terms are on the left hand side.
\frac{10}{21}x=r
Combine \frac{1}{3}x and \frac{1}{7}x to get \frac{10}{21}x.
\frac{\frac{10}{21}x}{\frac{10}{21}}=\frac{r}{\frac{10}{21}}
Divide both sides of the equation by \frac{10}{21}, which is the same as multiplying both sides by the reciprocal of the fraction.
x=\frac{r}{\frac{10}{21}}
Dividing by \frac{10}{21} undoes the multiplication by \frac{10}{21}.
x=\frac{21r}{10}
Divide r by \frac{10}{21} by multiplying r by the reciprocal of \frac{10}{21}.
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