Can someone help me add logic such as OR, AND, or NOT to existing PHP to help validate..

[Brian]

...or process? Looked through some books I have and searched Google and this is what I have so far can someone help me add a OR, AND, or NOT to process or validate?

<?php
$val1 = isset($_POST['value']);
$val2 = 140;
$submit = isset($_POST['submit'])

if($submit) {
if(is_numeric($val1))
{
$val3 = $val1 * $val2;
}
else
$val3 = "Invalid number.";
}
?>
<form method="post" action="">
Enter estimated hours of work: <input type="text" name="value" /><br/>
Estimated cost of project: <input type="text" value="<?php
if(isset($val3))
echo $val3;
?>" name="result" disabled="disable"/><br/>
<input type="submit" value="Calculate" name="submit" />
</form>