Answer
$y$ does vary directly with $x$.
The constant of variation, $k$, is $-5$.
Work Step by Step
If $y$ varies directly with $x$, then the equation would take the form $y = kx$, where $k$ is the constant of variation.
To see if this equation is a direct variation equation, we would need to rewrite the equation such that $y$ is on the left-hand side. Subtract $5x$ from each side of the equation:
$$y = -5x$$
We can see that the equation does take the form $y= kx$; therefore, $y$ does vary directly with $x$.
The constant of variation, $k$, is the coefficient of the variable $x$. In this case, $k$ is $-5$.
