Transportation : car bus deductions File "python", line 16 cost=days * 40 ^ IndentationError: expected an indented block

Community
1 
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):
    if days < 3:
    cost=days * 40
    return cost
        elif days >= 7:
           return cost -= 50
        elif days >= 3:
           return cost -= 20
        return cost