- preg_match: documentation ( source)
<?php
$strings = [
'Sunscreen 25g (200 Quantity)',
'Lubricant 100ml (50 Quantity)',
'WD-40 100ml (75 Quantity)',
];
foreach ($strings as $string) {
echo (preg_match('~\(\K\d+~', $string, $match) ? $match[0] : 'no quantity') . "\n";
}