//1st implementation
public function out_av($v1, v2)
{
    return 'The average of'.$v1.' and '.$v2.'is: '.calc_av($v1,$v2)
}

public function calc_av($v1, v2)
{
    return ($v1+$v2)/2
}



//2st implementation
public function out_av($v1, v2)
{
    return 'The average of'.$v1.' and '.$v2.'is: '.($v1+$v2)/2
}