Getting & Calculating Data from Multiple Web Blocks

I have used a web block to create a row with one input (Qty), a combobox with a list of items to choose from and an expression that outputs the price of the selected item from the combobox multiplied by the qty. This is all similar to the information a server at a restaurant would enter onto a guest check while taking their customers order (i.e. qty, item & price multiplied by the qty). You can view what I have done here;

I then placed this web block on the screen 5 times in order to be able to add several items to the check. Everything is working correctly, except I have been unable to take the total sum of all the items purchased and output that sum to the expression on the screen. I am using the Notify and OnNotify actions to send the data from the web block to the screen, but unfortunately it only send the data for the price of the current line I am updating and not all of the lines. 

Any advice of help would be much appreciated. I have also attached the OML file to this post.

Hi RC, each web block is independent, and knows nothing about the other web blocks. You need to notify also on selection of the item, so you can send the item price and/or total for that line, and keep track of the total on the main screen.