Evaluate the expression for w = –3 and x = –3.9.

To evaluate the expression \( w^2x - x \) for \( w = -3 \) and \( x = -3.9 \), we start by calculating \( w^2 \).

1. Calculate \( w^2 \): \[ w^2 = (-3)^2 = 9 \]

2. Substitute \( w^2 \) and \( x \) into the expression: \[ w^2x - x = 9(-3.9) - (-3.9) \]

3. Calculate \( 9(-3.9) \): \[ 9 \times -3.9 = -35.1 \]

4. Now substitute back into the expression: \[ -35.1 - (-3.9) = -35.1 + 3.9 \]

5. Finally, perform the subtraction: \[ -35.1 + 3.9 = -31.2 \]

So, the value of the expression \( w^2x - x \) is \(\boxed{-31.2}\).