insert whitespaces into string

[kee]

i m a php newbie
i trying insert whitespaces into a string for every 3 characters but fail...
so i need help pls, thank you

eg:
$string = 'AGTCCATGTAC'';

into

$string='AGT CCA TGT AC';

[Installer]

Try:

$str = 'abcdefghijklmnopqrs';
$str2 = chunk_split($str, 3, ' ');
echo $str2;