Subtract two numbers and enter result into DB?

[SEVIZ]

I have two numbers in a php script.  They are called into my process php file via post.  Inside the process php file I need to subtract the one from the other like this:

$_POST["MAXAMOUNT"]  -  $_POST["TOTAL"]  =  Number here

 

Once the math is done I want to run a query to a database to insert that value into a row depending on the ID that submitted the form. 

 

So in all here is what I am trying to do in basic terms. 

$_POST["MAXAMOUNT"]  -  $_POST["TOTAL"]  =  Number here

Number here = $number
$_POST["ID"] = $id


$query="INSERT INTO orderform (balance) WHERE id='$id' VALUES ('$number')";

 

Is that kinda right?  Am I on the right path?  Any help is appreciated!

[daveoffy]

you are on the right path.

 

$money = $_POST['MAXAMOUNT'] - $_POST['TOTAL'];
$id = $_POST['ID'];
$qry = "INSERT INTO 'orderform' (money) VALUES('$money') WHERE id='$id'"
$result = @mysql_query($qry);