#### Answer

The constant of variation is $\frac{1}{5}$.
The direct variation equation is $y=\frac{1}{5}x$.

#### Work Step by Step

$y=kx$
$y=4; x=20$
$4=k(20)$
$\frac{4}{20}=k$
$\frac{1}{5}=k$
The constant of variation is $\frac{1}{5}$.
The direct variation equation is $y=\frac{1}{5}x$.