Chapter 7 - Functions and Graphs - 7.5 Formulas, Applications, and Variation - 7.5 Exercise Set - Page 485: 4

$b$

RECALL: An inverse variation has an equation of the form $y=\frac{k}{x}$ where $k$ is the constant of variation (constant product). Thus, the given equation represents an inverse variation where $y$ varies inversely with $x$. Therefore, the answer is $b$.