Exercise 1: Why a Laptop's Private and Public IPs Differ — Possible Solution
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Explanation:

Per the chapter, "a home router... has one public IP address facing
the internet, while every device behind it -- laptops, phones, smart
TVs -- gets a private 192.168.x.x (or similar) address that only means
something inside that one household's network." The laptop's private
address (192.168.1.42) is only meaningful and only routable within the
local home network itself -- per the chapter's own earlier section,
private ranges "are never routable on the public internet." If the
laptop tried to use that private address directly to communicate with
a server out on the internet, the response would have no way to find
its way back, since 192.168.x.x addresses mean nothing to internet
routers outside the home network.

The mechanism responsible for the difference is NAT (Network Address
Translation). Per the chapter, "when a device behind the router sends
a packet outward, the router rewrites the packet's source IP and port
to its own public IP, and tracks the mapping." So when the laptop
sends a request out to a "what is my IP" website, the router
intercepts that outgoing packet and replaces the laptop's own private
source address with the router's single public address before sending
it onward. From the website's own perspective, the request appears to
have come directly from the router's public IP -- which is exactly the
address the website reports back as "your IP." The laptop's own real,
private address (192.168.1.42) is never visible to anything outside
the home network at all; only the router's public IP is.

WHY THIS WORKS AS AN ANSWER
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This explains both why the private address alone couldn't work
directly on the internet (it isn't routable there) and identifies NAT
specifically as the mechanism that substitutes the router's public
address for outgoing traffic, using the chapter's own description of
how that rewriting actually happens.