Subnets
IP Range Calculator - http://jodies.de/ipcalc?host=159.231.0.0&mask1=22&mask2=
IP Subnetting Made Easy (read very good) - http://www.techrepublic.com/article/ip-subnetting-made-easy/6089187
Enter an IP address to find out info of the owner and what Internet address block they own - https://www.arin.net/