$re = '/(\d+)\s+([A-Z]+)(\d+)\s+(\w+)/';
$str = '6876786786 GFS8978976 I
6786786767 DDF78676 I
4343245443 SBSSK67676 I
8393372263 SBSSK56565 I
6545434347 DDF7878333 I
6757650000 SBSSK453 I';
$subst = "$1+$2+$3+$4";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php