I was currently doing the exercise Taking a vacation 5/7, in my opinion it is not very difficult and I thought Idid not make a mistake. After I pushed the save and submit button I received an error. After the former tasks (1/7 - 4/7) were all right, I assumed that I did a mistake during the step where you add the cost. After I tried a bit i just randomly switched the function a bit up, wich worked. But I cannot explain to me why it did not work before: Here ist the code and thank you for your help

```
def hotel_cost(nights):
return 140*nights
def plane_ride_cost(city):
if city =="Charlotte":
return 183
if city =="Tampa":
return 220
if city =="Pittsburgh":
return 222
if city =="Los Angeles":
return 475
def rental_car_cost(days):
cost = days*40
if days >= 7:
return cost-50
elif days >=3 and days <= 7:
return cost-20
else:
return cost
def trip_cost (days, city):
return hotel_cost(days) + rental_car_cost(days) + plane_ride_cost(city)
Error: trip_cost('Charlotte', 5) raised an error: unsupported operand type(s) for -: 'str' and 'int'
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#Thats how it works (I can't explain why, I only changed the order of city and days)
def trip_cost (city, days):
return hotel_cost(days) + rental_car_cost(days) + plane_ride_cost(city)
```