Solve for b
b=\frac{f-5}{20}
Solve for f
f=20b+5
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40b=2f-10
Swap sides so that all variable terms are on the left hand side.
\frac{40b}{40}=\frac{2f-10}{40}
Divide both sides by 40.
b=\frac{2f-10}{40}
Dividing by 40 undoes the multiplication by 40.
b=\frac{f}{20}-\frac{1}{4}
Divide -10+2f by 40.
2f=40b+10
Add 10 to both sides.
\frac{2f}{2}=\frac{40b+10}{2}
Divide both sides by 2.
f=\frac{40b+10}{2}
Dividing by 2 undoes the multiplication by 2.
f=20b+5
Divide 40b+10 by 2.
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