When \( y \) varies directly with \( x \), we can express this relationship as:
\[ y = kx \]
where \( k \) is the constant of variation.
Given \( x = 4 \) and \( y = -24 \), we can substitute these values into the equation to find \( k \):
\[ -24 = k(4) \]
To solve for \( k \), divide both sides by 4:
\[ k = \frac{-24}{4} = -6 \]
Thus, the constant of variation is \( k = -6 \).