When you click on "check out" in my oscommerce store i get this message on the top of the page:

Warning: Division by zero in C:\Inetpub\wwwroot\catalog\includes\classes\shippi ng.php on line 61

Warning: Division by zero in C:\Inetpub\wwwroot\catalog\includes\classes\shippi ng.php on line 62


I understand nothing, please help me!