What to do after applying the Magic Number Method

BasedThot

Lets say you have an IP of 165.245.77.12 and a subnet of 255.255.240.0. After applying the Magic Number Method you find out you have a first host of 165.245.64.1 and a last host of 165.245.79.254. But if we have a question that gives you that same IP address and subnet and they want for example 4 networks with at least 50 host addresses(I'm assuming there will be questions like this, yes?), how would you go about deducing the answer? Also any good sources for subnetting would be greatly appreciated. Grasping this subject is the one thing holding me back from taking the exam. Professor Messer's videos have helped me greatly thus far but his explanation on subnetting is just missing the mark for me.  

JDMurray

IP subnetting has several different ways to conceptualize what's happening. It really didn't sink in with me until I learned to visualize the IPv4 address space as a tree map. When I imagined how the map visually changed when the netmask changed (/1, /2, /8, /15, /16, etc.) it really clicked for me. Suddenly I could "see" why changing from /16 to /15 both doubled the number of hosts per subnet and halved the number of available subnetworks. The address points in the IPv4 space stayed the same while it was the borders around the points that were re-drawn.