BLOCKCHAIN & WEB3 FUNDAMENTALS - Chapter 7, Exercise 3 Solution
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Tracing a Real Bitcoin Payment Through Every Step, Chapter by Chapter

PROBLEM
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Walk through this chapter's own five-step transaction flow for a real
Bitcoin payment, naming specifically which earlier chapter's own
material each step relies on (Chapter 2, 3, 4, or 5).

SOLUTION
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STEP 1: CONSTRUCT THE TRANSACTION
Relies on: CHAPTER 5 (the UTXO model). The wallet selects one or more
of your existing UTXOs as inputs and builds the new outputs - a
payment to the recipient's address, plus a "change" output back to
yourself if the input's value exceeds what you're sending, exactly as
Chapter 5's own worked example described.

STEP 2: SIGN IT
Relies on: CHAPTER 2 (digital signatures / public-key cryptography).
The wallet uses your private key to produce a valid ECDSA signature
over the transaction data. This proves you're authorized to spend the
UTXOs being consumed, without ever exposing the private key itself -
the exact sign-with-private-key, verify-with-public-key process
Chapter 2 established.

STEP 3: BROADCAST IT
Relies on: CHAPTER 2 again, from the verification side this time.
Nodes receiving the broadcast transaction independently check the
signature against your public key before relaying it onward - the
"anyone can verify without needing the private key" property from
Chapter 2's own digital-signature explanation.

STEP 4: GET INCLUDED IN A BLOCK
Relies on: CHAPTER 4 (proof-of-work / mining). A miner assembles
pending transactions, including this one, into a candidate block, and
races to find a valid nonce that satisfies the network's current
difficulty target - exactly the mining process Chapter 4 described.

STEP 5: CONFIRM
Relies on: CHAPTER 3 and CHAPTER 4 together. As more blocks are mined
on top of the block containing this transaction, each new block adds
another layer of accumulated proof-of-work protecting it, per Chapter
3's own chaining/tamper-evidence mechanism and Chapter 4's own
"buried deeper equals more secure" reasoning - making the transaction
progressively harder for anyone to reverse.

ANSWER: Constructing the transaction relies on Chapter 5's UTXO model;
signing and broadcasting rely on Chapter 2's digital signatures (both
the signing and verifying sides); getting included in a block relies
on Chapter 4's proof-of-work mining process; and confirming relies on
Chapter 3's chaining mechanism combined with Chapter 4's own
accumulated-work security reasoning.

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WHY THIS WORKS AS AN ANSWER

This correctly maps every one of the chapter's five transaction steps
back to the specific, real mechanism from an earlier chapter that
actually makes that step work, rather than treating "how a transaction
works" as a standalone process disconnected from the rest of the
course.