If you have a list of things and you want to perform the same function on each thing in your list then the Map function is usually a good choice.
Each of your things is a list and you want the total of that. The Total function looks like what you want.
So the result is
Read the help pages for Map and Total and see if you can make sense of those now that you have seen an example.
Substitute your own for data and see if it works