please help on this one?

Answer:
[tex]\large\boxed{B.\ 0.4}[/tex]
Step-by-step explanation:
[tex]Height=\dfrac{Constant}{Width}\qquad\text{multiply both sides by}\ Width\neq0\\\\Constant=Height\cdot Width[/tex]
[tex]\text{Select any point from the graph}\to(0.5,\ 0.8)\\\\Width=0.5,\ Height=0.8.\\\\\text{Substitute:}\\\\Constant=0.5\cdot0.8=0.4[/tex]