#### Answer

The constant of variation is $\frac{3}{2}$.
The direct variation equation is $y=\frac{3}{2}x$.

#### Work Step by Step

$y=kx$
$y=6; x=4$
$6=k(4)$
$\frac{6}{4}=k$
$\frac{3}{2}=k$
The constant of variation is $\frac{3}{2}$.
The direct variation equation is $y=\frac{3}{2}x$.