taking a vacation, pulling it all together

oops, try again. hotel_cost(0) returned None instead of correct value 0

when working up to this point, the code for hotel_cost worked and now it's not. doesn't make any sense.

i have even tried not to have the sum = line, just the return "plane..., hotel..., car...'

getting frustrated

```
def hotel_cost(nights):
if nights > 0:
return 140 * nights
def plane_ride_cost(city):
if city == "Charlotte":
return 183
elif city == "Tampa":
return 220
elif city == "Pittsburgh":
return 222
elif city == "Los Angeles":
return 475
else:
return "You don't want to go there."
def rental_car_cost(days):
if days >= 7:
return days * 40 - 50
elif 3 <= days < 7:
return days * 40 - 20
else:
return days * 40
def trip_cost(city, days):
sum = plane_ride_cost(city) + rental_car_cost(days) + hotel_cost(days)
return sum
```