Solve for A
A=\frac{129-7B}{5}
Solve for B
B=\frac{129-5A}{7}
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5A=129-7B
Subtract 7B from both sides.
\frac{5A}{5}=\frac{129-7B}{5}
Divide both sides by 5.
A=\frac{129-7B}{5}
Dividing by 5 undoes the multiplication by 5.
7B=129-5A
Subtract 5A from both sides.
\frac{7B}{7}=\frac{129-5A}{7}
Divide both sides by 7.
B=\frac{129-5A}{7}
Dividing by 7 undoes the multiplication by 7.
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