Solve for a
a=13-b
Solve for b
b=13-a
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3a=39-3b
Subtract 3b from both sides.
\frac{3a}{3}=\frac{39-3b}{3}
Divide both sides by 3.
a=\frac{39-3b}{3}
Dividing by 3 undoes the multiplication by 3.
a=13-b
Divide 39-3b by 3.
3b=39-3a
Subtract 3a from both sides.
\frac{3b}{3}=\frac{39-3a}{3}
Divide both sides by 3.
b=\frac{39-3a}{3}
Dividing by 3 undoes the multiplication by 3.
b=13-a
Divide 39-3a by 3.
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