InfoPath Dev

I am trying to initalise a textbox based on the selection of Multiple Selection List Box options. For example, Multiple box: Option A, Option B, Option C, Option D and if I select 'Option A/Option B' the textbox should be incremented by 2 and if any of the two is deseleted it should do -2 for each. For ...

How to get an option in Sharepoint item context menu to link to infopath form, passing it the URL of that page? Actually I need to display that URL in the form as hyperlink so that users can use to navigate to that particular library.