To solve for \( 8x \) when \( 2x = -4 \), we start with the given equation:
\[ 2x = -4 \]
Now, we want to determine the value of \( x \). We can do this by dividing both sides of the equation by 2:
\[ x = \frac{-4}{2} = -2 \]
Now that we have the value of \( x \), we can find \( 8x \):
\[ 8x = 8(-2) = -16 \]
Thus, the value of \( 8x \) is \( -16 \).