Multiply both sides by 2: $\displaystyle{2}\cdot{A}={2}\cdot\frac{{1}}{{2}}{b}{h}\usepackage{cmbright}\Huge\$

Simplify: $\displaystyle{2}{A}={b}{h}\usepackage{cmbright}\Huge\$

Divide both sides by b : $\displaystyle\frac{{{2}{A}}}{{b}}=\frac{{{b}{h}}}{{b}}\usepackage{cmbright}\Huge\$

Simplify: $\displaystyle\frac{{{2}{A}}}{{b}}={h}\usepackage{cmbright}\Huge\$