yeah

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<pre>
	<form action = "Com.php" method="post">
		Input total sales: <input type="text" name="txtSales">
		Type 1: <input type="checkbox" name="chkType" value="1">
		Type 2: <input type="checkbox" name="chkType" value="2">
		Type 3: <input type="checkbox" name="chkType" value="3">
		Type 4: <input type="checkbox" name="chkType" value="4">
		<input type="submit" name="btnSubmit" value="Submit">
	</form>
	<?php
		if(isset($_POST["btnSubmit"]))
		{
		$sales = $_POST["txtSales"];
		$types = $_POST["chkType"];


				if($types==='1'){
				$amount = $sales*0.07;
				if($amount<400)
					echo 400;
				else
					echo $amount;
				}
				if($types==='2'){
				$amount = $sales*0.1;
				if($amount<900)
					echo 900;
				else
					echo $amount;
				}
				if($types==='3'){
				$amount = $sales*0.12;
					echo $amount;
				}
				if($types==='4'){
					echo 250;
				}
			}
		?>
	</pre>
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