Convert string to number format

Hello,

Thanks for you plugin. Iam tring to calculate included GST price in invoice page only. Below is my code.

<tr>
	<td>18% GST Amout</td>
	<td></td>
	<td class="price">
<?php 
  $replace_currency_symbol = str_replace('₹', '', $item['order_price']); 
  $replace_comma_in_price = str_replace(',', '', $replace_currency_symbol); 
  $Price = (float)$replace_comma_in_price;
  $amount = ($Price*18)/118; 
  echo round($amount,2); 
?>
       </td>
</tr>

Still the price format is not changing to number format. How to change or number format.