How do I subtract 3 weeks from a variable?

[dmirsch]

I have the following code:

		//DETERMINES ASL POLICY
	if ($perfRow['ASL']=='ToArrange'){ 
	$ASLdate = $perfRow['startDateTime'];
	$ASLconfirm = strtotime($ASLdate-'21 days');
		echo "<!--[ASL=ToARRANGE--><p>An ASL Interpreted performance of this event is offered on".date("l, F j",strtotime($perfRow['startDateTime']))." at ".date("g:i a",strtotime($perfRow['startDateTime'])).".<br />Please contact me by ".date("l, F j",strtotime($ASLconfirm))." to confirm this service.</p>";
	}

What I need is that if the ASL is "To be Arranged" there is a date that lists for $ASLconfirm that is three weeks prior to $ASLdate.

The code above gives me the following:

An ASL Interpreted performance of this event is offered on Friday, September 28 at 7:30 pm.

Please contact me by Wednesday, December 31 to confirm this service.

As you can see from the output the December date is NOT three weeks prior to the September date.

Where did I go wrong in my coding?

[marcus]

$ASLconfirm = date("l, F j", strtotime($ASLdate) - 1814400);

[dmirsch]

YEAH! Thanks -- that worked, but can you now tell my why "1814400"?

[marcus]

1814400 = 3600 * 24 * 21 = 3 weeks in seconds.

[dmirsch]

Thanks mgallforever!