Exercise 3: Finding Which Service Drove a 20% Bill Increase — Possible Solution
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The real, correct tool here is Cost Explorer. It's specifically
designed to analyze real spend over time, broken down by dimensions
like service, account, or tag -- exactly the "where did this
increase actually come from" question being asked.

CloudWatch wouldn't answer this question because it isn't a cost
analysis tool at all -- it's built to answer "is this resource
healthy and performing correctly right now" (CPU, network, alarms,
logs), not "how much did we spend, and on what." CloudWatch has no
real concept of billing or cost breakdown by service built into its
own metrics and alarms.

ANSWER: Cost Explorer is the right tool, since it's purpose-built to
break down real spend by service (and other dimensions) over time,
directly answering which specific service drove the increase.
CloudWatch alone wouldn't help here because it monitors resource
health and performance, not cost -- the two tools answer genuinely
different real questions, as the chapter's own comparison table lays
out directly.

WHY THIS WORKS AS AN ANSWER
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This correctly picks the tool matched to the specific real question
being asked (a cost-attribution question, not a health/performance
question), and explains WHY the other tool doesn't apply rather than
just naming the right one -- reinforcing the chapter's own point that
CloudWatch, Cost Explorer, and Budgets are three genuinely different
tools, not interchangeable ways to "monitor AWS."