Doing this as an audio exercise is slightly confusing when it's the man saying "obrigada"! I thought I heard "obrigada" but then typed "obrigado" anyway because it was the guy saying it rather than the lady! It just threw me. Would help a little if the right voices said the correct words.
Obrigado if said by a man, obrigada if said by woman
P.S. Even though this space should always be used by you to get answers to pressing language questions related to the sentence, I urge not to think of us as automatons: we're students just like you, all part of a community of equals trying to help each other out in their respective learning journeys; as such, words like "Please", "Thank you" (and even a question mark from time to time) are always welcome to foster a good learning environment in the forums.
Thank you for understanding, and good luck with your studies :)
My student collegues, you are right: obrigado is for man, obrigada for woman. But even a man can "read" a female answer. For example if a man reads a book and there is quotation like this. Or, if a Portuguese/Brasilian teacher explains to his female student, how she should say "thank you". Am i right?