print(calculate_tax(10.0, 0.13))

def calculate_tax(bill: float, tax_rate: float) -> float:
    """Return the amount of tax to be paid after tax_rate
    is applied to bill.
    
    Precondition: 0.0 <= tax_rate <= 1.0
    
    >>> calculate_tax(10.0, 0.13)
    1.3
    >>> calculate_tax(20.0, 0.8)
    16  
    """
    
    tax = bill * tax_rate
    return tax

print(calculate_tax(10.0, 0.13))