String 'questionusedinquiz' contains a invalid placeholder

When editing multianswer question (with the existing attempts), Placeholders is not replaced with correct values.
Need fix the string 'questionusedinquiz' in qtype_multianswer.php like this
$string['questionusedinquiz'] = 'This question is used in {$a->nbofquiz} quiz(s), total attempt(s) : {$a->nbofattempts}';