the error is:

Oops, try again. trip_cost('Pittsburgh', 1) raised an error: 'function' object is not iterable

I have no idea what iterable even means but heres my code:

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

else:

print "invalid city name!!"

def rental_car_cost(days):

cost = days * 40

if days >= 7:

cost -= 50

elif days >= 3:

cost -= 20

return cost

def trip_cost(city, days):

return sum (nights) + (city) + (days)