kalkulaator.php
<form method="post" action="arvutus.php">
<input type="text" name="value">
<input type="submit">
</form>
arvutus.php
$value = $value-($value*0.04-($value*0.04-144)*0.21);
echo "Result is " . $_POST["value"] . "";
如何使用 value 进行这些计算?