Suppose Z Varies Directly as X and Inversely as the Square

Multiple Choice

Suppose z varies directly as x and inversely as the square of y. If x is doubled and y is tripled, what happens to z?

A) $\mathrm { z }$ is one-sixth as large as before
B) $z$ is six times as large as before
C) $\mathrm { z }$ is multiplied by $\frac { 1 } { 18 }$
D) $\mathrm { z }$ is multiplied by $\frac { 2 } { 9 }$