Answer:
[tex]\large\boxed{b=\dfrac{2A}{h}}[/tex]
Step-by-step explanation:
[tex]h=\dfrac{2A}{b}\qquad\text{multiply both sides by}\ b\neq0\\\\hb=2A\qquad\text{divide both sides by}\ h\neq0\\\\b=\dfrac{2A}{h}[/tex]