I'm stuck at Taking A Vacation, exercise 7.

I'm just confused at calling functions. Why does the following work in the semi last line:

hotel_cost(days)

when the original is

def hotel_cost(nights):

return 140 * nights

Does that mean days will replace nights? but in that case what happens to return 140 * nights? Does it become

hotel_cost(days):

return 140 * days

???

Thanks.

```
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):
cost = 40 * days
if days >= 7:
cost -= 50
elif days >= 3:
cost -= 20
return cost
def trip_cost(city, days, spending_money):
return rental_car_cost(days) + hotel_cost(days) + plane_ride_cost(city) + spending_money
print trip_cost("Los Angeles", 5, 600)
```