How to use result of query as a variable?

So I have a content management site set up, but I’m stuck on one part. I have a query

Select `email` FROM author WHERE IN(SELECT authorid FROM job WHERE id = '$_POST[id]')

. I’m a beginner in PHP and SQL. Basically I need the query to run, it will come out with one result and I need that to be where the email is sent to. This is the existing code I have for sending out the email

$subject = " Job Application Confirmation";

$message = "Hello $_POST[name] , \r\rYou, or someone using your email address, has applied for the job: $text Using the Resource Locator at Keep this as future reference. \r\r Full Name: $_POST[name] \r Location: $_POST[location] \r Email: $_POST[email] \r Additional Information: $_POST[info] \r Job ID: $id  \r Job Name: $text  \r \r Expect a response shortly. \r\r Regards, Team";

$headers = 'From: Team <[email protected]>';

    'Reply-To: [email protected]' . "
" .

    'X-Mailer: PHP/' . phpversion();

$to1      = '[email protected]';

mail($to1, $result, $message, $headers);

Thanks in Advance!