Please i need help, i cant figure out what to do with the spending_money argument, or what to do with it,

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