Good job.. Two things...
1. CIDR is basically a short-hand method of abbreviating a subnet mask...
255.255.0.0 = /16
255.255.255.0 = /24
255.255.255.128 = /25
255.255.255.192 = /26
255.255.255.252 = /30
You can get this by counting the 1's or network bits...
11111111.11111111.11111111.11100000 = 255.255.255.224 or /27
2. In the above example you borrowed 6 bits..
"6 bits
1111.1111.11111111.11111100
255.255.255.252
low inc = 4"
Those 6 bits represent 64 subnets..
2, 4, 8, 16, 32, 64...
You listed 20 subnets above and x.x.x.148 - .151 is the 20th subnet.. You still have a ways to go.. See if you can figure out what the last subnet is...
6. What is the network address of the last available subnet? (Take your time with this one! It's tricky!)
B Haines
CCNA R&S, ETA FOI