Find a Mathematical Model Representing the Statement $z = \frac { 3 x ^ { 2 } } { 4 y }$

Multiple Choice

Find a mathematical model representing the statement.(Determine the constant of proportionality.)
Z varies directly as the square of x and inversely as y.(z = 36 when x = 9 and y = 3.)

A) $z = \frac { 3 x ^ { 2 } } { 4 y }$
B) $z = \frac { 4 x } { 3 y }$
C) $z = \frac { 4 x ^ { 2 } } { 3 y }$
D) $z = - \frac { 3 x ^ { 2 } } { 4 y }$
E) $z = - \frac { 4 x ^ { 2 } } { 3 y }$