When you see a question that you want to answer with a hub -
FIRST - click to 'answer'
at the bottom of the text box it says 'make a hub about it' or 'submit answer'
if you want to answer with a hub you have to click 'make a hub about it'
if you just want to answer the question - fill in the text box and then click 'submit answer'
Is that what you meant by linking a hub to an answer? If you meant including a hub as a reference in your answer why not just cut and paste a link? However, including hub links in answers and forums seems to be a no no in regard to HP etiquette