error $data['payment_amount']) เขียนอย่างไรให้ถูกค๊ะ

if($data['payment_amount'] < 100)
	{
     // Fee Rate 10%
		$fee_all = "( ($data['payment_amount']) * (0.1) )";
	}
elseif($data['payment_amount'] >= 100 AND $data['payment_amount'] < 1500)
	{
     // Fee Rate $10 + 5.0% of Total Price over $100
		$fee_all = "( 10 + ( ($data['payment_amount']) * (0.05) ) )";
	}
else
	{
     // Fee Rate $80 + 3.0% of Total Price over $1500
		$fee_all = "( 80 + ( ($data['payment_amount']) * (0.03) ) )";
	}