Joy, your answers look fine to me in terms of normal, everyday speech but there are other possibilities as well.
Your 'answer' (question!) "What would you prefer" is correct but perhaps your teacher is looking for something more precise, such as offering two alternatives, like tea or coffee, in the question. 'Would you prefer tea or coffee?"
In the second one, again I think your question is fine in everyday speech but your teacher might be looking for you to use a quantity in your question to match the quantity ("not very much") in the answer. So, the second one might be more correct as "How much do you know about the Australian market?"