[Python] Unsupported format string passed to NoneType.__format__

The initial problem I started with is:

Write a function so that the main program below can be replaced by the simpler code that calls function mph_and_minutes_to_miles().

miles_per_hour = float(input())
minutes_traveled = float(input())
hours_traveled = minutes_traveled / 60.0
miles_traveled = hours_traveled * miles_per_hour

print('Miles: {:f}'.format(miles_traveled))


Sample output with inputs: 70.0 100.0
Miles: 116.666667
​

The code I have written for it so far is:

def mph_and_minutes_to_miles(miles_per_hour,minutes_traveled):
hours_traveled=minutes_traveled/60.0
miles_traveled=hours_traveled*miles_per_hour
print('Miles: {:f}' .format(miles_traveled))
miles_per_hour = float(input())
minutes_traveled = float(input())

print('Miles: {:f}'.format(mph_and_minutes_to_miles(miles_per_hour, minutes_traveled)))


The error message it produces is:

Exited with return code 1.
Traceback (most recent call last):
File "main.py", line 8, in <module>
print('Miles: {:f}'.format(mph_and_minutes_to_miles(miles_per_hour, minutes_traveled)))
TypeError: unsupported format string passed to NoneType.__format__


After reviewing the code a few times I still can not seem to figure out how to rectify it.

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