$a = "3dollars";
$b = 20;
echo $a += $b;
print($a += $b);
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It casts '3dollars' as a number, getting $a = 3.
When you echo, you add 20, to $a, so it prints 23 and $a = 23.
Then, when you print, you again add 20, so now $a = 43.
