Write an Equation to Describe the Variation $x$ And Inversely As $y$

Multiple Choice

Write an equation to describe the variation. Use k for the constant of proportionality.
-w varies directly as $x$ and inversely as $y$ .

A) $w + x - y = k$
B) $w x y = k$
C) $w = \frac { k x } { y }$
D) $w = \frac { k y } { x }$