5*(5*4x)

To simplify the expression \( 5 \times (5 \times 4x) \), follow these steps:

1. First, simplify the inside of the parentheses: \( 5 \times 4x = 20x \).
2. Now, you have \( 5 \times 20x \).
3. Multiply this out: \( 5 \times 20x = 100x \).

So, the simplified expression is \( 100x \).