Challenge 1: Build and Dereference — Possible Solution
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use strict;
use warnings;
use feature 'say';

my @numbers = (10, 20, 30);
my $array_ref = \@numbers;

say $array_ref->[1];
say scalar(@$array_ref);

Output:
20
3

WHY THIS WORKS AS AN ANSWER
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my @numbers = (10, 20, 30); reuses a plain array declaration from
Course 1, Chapter 3, and my $array_ref = \@numbers; reuses the
chapter's own backslash-reference-creation syntax exactly — $array_ref
is a scalar pointing to @numbers, not a copy of its contents.

$array_ref->[1] reuses the chapter's own idiomatic arrow
dereferencing syntax, retrieving the element at index 1 (the second
element, 20) out of the array @numbers points to — the "modern,
idiomatic" form the chapter recommends over the classic
${$array_ref}[1] equivalent.

scalar(@$array_ref) reuses @$array_ref — a shorthand equivalent to
the chapter's own @{$array_ref} classic dereference syntax, without
the braces — to get back the WHOLE array (all 3 elements) that
$array_ref points to, and scalar() (reused from Course 1, Chapter 3)
forces it into scalar context to report the count, 3, rather than the
elements themselves.