Solve for x
x=\frac{7-y}{3}
Solve for y
y=7-3x
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9x=21-3y
Subtract 3y from both sides.
\frac{9x}{9}=\frac{21-3y}{9}
Divide both sides by 9.
x=\frac{21-3y}{9}
Dividing by 9 undoes the multiplication by 9.
x=\frac{7-y}{3}
Divide 21-3y by 9.
3y=21-9x
Subtract 9x from both sides.
\frac{3y}{3}=\frac{21-9x}{3}
Divide both sides by 3.
y=\frac{21-9x}{3}
Dividing by 3 undoes the multiplication by 3.
y=7-3x
Divide 21-9x by 3.
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