Absolutely no idea how to do this. I've searched online and couldn't find an example where it uses Nets.
A lot of us emailed the professor about this problem explaining it's nothing like what we learned and his generic reply didn't help at all.
Maybe somebody here might be able to help me out.
Quote (Professor)
I've received several emails re: question 2 and some confusion it has caused. That was not my intention.
This question comes from another (edition of the) book, and therefore it uses a slightly different notation. But it is similar in spirit to figure 20.6. Just think if the numbers under the 'Net' columns as Net IDs that correspond to which networks can be reached (rather than the router that connects the network to the rest of the Internet -- which is our textbook's interpretation).
I hope this helps.