In order to solve for "b", you have to find an expression b = ...
To do it, first, subtract 4a from both sides of the equation.
[tex]\begin{gathered} c-4a=4a+4b-4b \\ c-4a=4b \end{gathered}[/tex]Now, divide both sides by 4:
[tex]\begin{gathered} \frac{c-4a}{4}=\frac{4b}{4} \\ \frac{c-4a}{4}=b \end{gathered}[/tex]Which is the same as:
[tex]b=\frac{c-4a}{4}[/tex]Answer:
[tex]b=\frac{c-4a}{4}[/tex]