Exercise 1: Stopped vs. Terminated, and the "Still Being Billed" Mystery — Possible Solution
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The difference:

A STOPPED VM is powered off but still EXISTS -- its configuration and,
critically, its attached storage volume are preserved exactly as they
were, ready to be started again at any time. A TERMINATED (or deleted)
VM is gone permanently -- the instance itself and, usually, its
storage are removed entirely, recoverable only if a snapshot was taken
beforehand.

Why a "stopped" VM can still generate charges:

Stopping a VM only stops the COMPUTE charges -- you're no longer being
billed for the CPU/RAM the running instance was consuming. But per
this chapter's own point, the VM's attached storage volume is a
SEPARATE billed resource that continues to exist (and continues
costing money) regardless of whether the VM itself is running or
stopped. A customer insisting their VM is "stopped, not running" is
correct about the compute side -- but if the storage volume attached
to it was never deleted, that storage is still being billed every
single day the VM sits in the stopped state, which is exactly what
explains the continued charges they're seeing.

The correct next step for a customer who genuinely wants to stop ALL
charges (not just compute) would be to either terminate the instance
entirely, or explicitly delete the unused storage volume if they don't
need to preserve its contents -- simply stopping the VM was never
enough to eliminate 100% of the associated cost.

WHY THIS WORKS AS AN ANSWER
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This directly applies the chapter's own tip-box, which names this
exact scenario as "one of the most common billing-support tickets in
practice" -- the key insight being that compute and storage are
billed as two SEPARATE resources, and stopping only addresses one of
them.