if you look at your cost you accidentally put a = in front of the 20
Two things. 1) I believe you need to set your cost variable to 40 * days (similar to hotel_costs), and 2) I don't think you need the first return in your if statement, since the if/elif statements are just altering the total of the cost variable. I had a similar error, and those are the two changes I made to pass the exercise.
try this, it's working perfectly(I know it's not efficient , but there seems to be a problem with this topic)
elif day>=3: return (day*40)-20 else: return day*40