Write an Equation to Describe the Variation $r$ And the Cube Of

Multiple Choice

Write an equation to describe the variation. Use k for the constant of proportionality.
-q varies jointly as $r$ and the cube of $s$ .

A) $q = k + r + s ^ { 3 }$
B) $\mathrm { qrs } ^ { 3 } = \mathrm { k }$
C) $\mathrm { q } + \mathrm { r } + \mathrm { s } ^ { 3 } = \mathrm { k }$
D) $q = k r s ^ { 3 }$