5•(5•4x)

To simplify the expression \( 5 \cdot (5 \cdot 4x) \), you can follow the steps below:

1. Start by simplifying the inner expression: \[ 5 \cdot 4x = 20x \]

2. Now substitute back into the expression: \[ 5 \cdot (20x) \]

3. Finally, multiply: \[ 5 \cdot 20x = 100x \]

Thus, the simplified expression is: \[ 100x \]