Re: Mamá, ________ -Bien ¿y tú? Mum, how are you? -Good, and you?
In a test I just did, for the above question, I added: "¿cómo está?" but it was marked wrong.
I chose this, because in certain areas, children address their mother formally, so that is why I used the "formal" in this case. i know it is not common, but the test did say, some or all may be correct.
Thank you for your attention to this,
Nicole