https://www.codecademy.com/courses/python-beginner-P5YtY/1/4?curriculum_id=4f89dab3d788890003000096#

getting correct values for trip_cost but have error:

Oops, try again. trip_cost('Tampa', 8) raised an error: unsupported operand type(s) for -: 'str' and 'int'

Running the plane_ride_cost() by itself doesn't result in error.

Running trip_cost() with only plane_ride_cost() also doesn't result in error.

Error only appears if I run trip_cost() together with all the other function

can anyone explain the error?

```
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
else:
return "xxxxxx"
def rental_car_cost(days):
cost = 40 * days
if days >= 7:
return cost - 50
elif days >= 3 and days < 7:
return cost - 20
else:
return cost
def trip_cost(a, b):
return hotel_cost(a) + plane_ride_cost(b) + rental_car_cost(a)
print trip_cost(1, "Charlotte")
```