If Y Varies Directly as X, Find a Linear Function $f ( x ) = \frac { 8 } { 3 } x$

Multiple Choice

If y varies directly as x, find a linear function which relates them.
-y = 24 when x = 9

A) $f ( x ) = \frac { 8 } { 3 } x$
B) $f ( x ) = 3 x$
C) $f ( x ) = x + 15$
D) $f ( x ) = \frac { 3 } { 8 } x$