This is a good question and the book side steps the question
NAT
NAT (Network Address Translation) is a 1 for 1 translation of Private Addresses for Public Addresses
It Does Not Save you any IP Addresses
Inside
Outside
10.1.1.10
10.1.1.11
10.1.1.12
11.1.1.10
11.1.1.11
11.1.1.12
Aside from some debatable and somewhat superficial security enhancements, NAT is used to explain how the wider Technology for PAT works, for example:
DNAT – Dynamic Nat
NAT with Dynamically assigned addresses from a pool of addresses
SNAT – Static Nat
NAT with Statically assigned addresses from a person
So Let's Focus on PAT