Challenge 3: Common Elements — Possible Solution
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a = [1, 2, 3, 4, 5]
b = [3, 4, 5, 6, 7]

common = sorted(set(a) & set(b))

print(common)

Output:
[3, 4, 5]

WHY THIS WORKS AS AN ANSWER
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set(a) and set(b) convert both lists into sets first, since the &
intersection operator from this chapter's set section only works
between sets, not lists directly.

set(a) & set(b) then reuses that exact intersection operator to find
the elements present in both sets — 3, 4, and 5 — automatically
discarding 1 and 2 (only in a) and 6 and 7 (only in b).

Because sets are unordered, the raw result of the intersection could
print in any order depending on Python's internal set implementation
— wrapping the whole expression in sorted() converts it back into an
ordered list AND guarantees a predictable, consistently sorted output,
which is what the challenge asks for.