Hi Thomas,
Not sure if you've seen any of these, but there are some good tutorials on YouTube for Subnetting. . .
https://www.youtube.com/watch?v=7t4CQdBhhMM - This guy does a lot of CompTIA tutorials (A+, Network+ etc)
https://www.youtube.com/watch?v=rs39FWDhzDs - Long, but detailed.
Lots more videos! https://www.youtube.com/results?search_query=subnetting
Stephen
