Answer:
[tex]r=\frac{3B}{f}-k[/tex].
Step-by-step explanation:
1. Write the expression.
[tex]B=(\frac{r+k}{3} )f[/tex]
2. Divide by f on both sides.
[tex]\frac{B}{f} =[(\frac{r+k}{3} )f]/f\\ \\\frac{B}{f} =\frac{r+k}{3}[/tex]
3. Multiply both sides by 3.
[tex]\frac{3B}{f} =r+k[/tex]
3. Substract k from both sides.
[tex]\frac{3B}{f}-k =r+k-k\\ \\\frac{3B}{f}-k =r[/tex]
4. Reorganize.
[tex]r=\frac{3B}{f}-k[/tex].
