Add value to a variable on each row of a table

I have a shopping cart which shows all the items in it, one per row. The items are pulled in from a data store but the values come from the database. I need to show the total at the bottom but don’t know how best to achieve this in Wappler.

I would normally create a variable and then add the line value to it so it is part of the loop.

How is that done in Wappler?