Write an Equation to Describe the Variation $z ^ { 4 }$

Multiple Choice

Write an equation to describe the variation. Use k for the constant of proportionality.
-a varies directly ay as $z ^ { 4 }$

A) a = k $k z ^ { 4 }$
B) a = $\frac { \mathrm { k } } { \mathrm { z } ^ { 4 } }$
C) z = $\frac { k } { a ^ { 4 } }$
D) z = k $\mathrm { ka } ^ { 4 }$