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

returns the error "3 days returns the cost of 120 instead of 100." It's almost like "cost - 20" isn't even working at all. I replaced it with "cost - 100" and it still said it's giving 120 instead of 100. Beyond that. When I did "cost = cost - 20" it said it was giving the result of 280.

It's either bugged, or I'm missing something.

I've had to change the math formulas multiple times. I didn't follow the example the first few times and quickly realized why my ways weren't viable. so it's not like I've been dealing with this exact issue for so long.