```python
def step_rate(amount: int, fixed: int, percent: int) -> int:
    """Return the charge for one step, rounding down."""
    base_charge = fixed + (amount * percent // 100)
    return base_charge

def rate_steps(amounts: list, fixed: int, percent: int) -> list:
    """Return the charge for each of several amounts."""
    return [step_rate(amount, fixed, percent) for amount in amounts]
```