使用Binding转换器在silverlight中显示和更新属性

I am using a converter class to display a property called noofweeks based on normal working hours(40), so for example if the value stored in database is 40 I am displaying 1 in the datagrid column, if it is 80 I am displaying 2, here is my XAML and converter codeI am using a converter class to display a prope