If Y Varies Directly as X, Find a Linear Function $y = 5$

Multiple Choice

If y varies directly as x, find a linear function which relates them.
- $y = 5$ when $x = 40$

A) $f ( x ) = \frac { x } { 8 }$
B) $f ( x ) = x + 35$
C) $f ( x ) = \frac { x } { 5 }$
D) $f ( x ) = 8 x$