Hello Stefanie,
The error message says your code doesn’t compute the answer correctly so there are some bugs. I have to make the same suggestions as in this topic so please take a look, and hopefully with them you will find some necessary variables are never used in your work. Those suggestions are useful in general for the rest of this specialization to help debugging your work.
Good luck with the assignments!
Cheers,
Raymond
PS: I will edit your post since sharing assignment code isn’t allowed here. Posting the error traceback is sufficient.