Will anyone tell me whats wrong?

i get this error

trip_cost('Charlotte', 8, 0) raised an error: unsupported operand type(s) for -: 'str' and 'int'

my code:

```
def hotel_cost(nights):
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

def rental_car_cost(days):

if days >= 7:

return 40 * days - 50

```
elif days >= 3:
return 40 * days - 20
elif days < 3:
return 40 * days
```

def trip_cost(days, city, spending_money):

return rental_car_cost(days) + hotel_cost(days) + plane_ride_cost(city) + spending_money