Taking a Vacation 4/7

#1 
def rental_car_cost(days):
  cost == days * 40
  if days >= 7:
  	return cost - 50
  elif days >= 3:
  	return cost - 20
  else:
    return cost

What is wrong with the code above?

#2

here:

cost == days * 40

two equal signs means check if equal, why would you check if costs equals 40 * days?

#3

Thanks so much! This is literally my first day coding, and with python. The syntax is entirely new and you help is greatly appreciated