[tex]A= \frac{1}{4}f(q+b) \ \ \ \ \text{[multiply both sides by 4]} \ \ \to \\ \\ 4A=f(q+b) \ \ \ \ \text{[divide both sides by f]}\ \ \to \\ \\ \frac{4A}{f} =q+b \ \ \ \
\ \ \ \ \text{[isolate q]}\ \ \to\\ \\ q= \frac{4A}{f}-b \ \ \ \ \ \ \ \ \ \leftarrow answer[/tex]
