Write an Equation to Describe the Variation $w$ Varies Jointly As $x$

Multiple Choice

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

A) $w = k + x + y ^ { 3 }$
B) $w = k x y ^ { 3 }$
C) $w + x + y ^ { 3 } = k$
D) $w x y ^ { 3 } = k$