You’ll need to use “List.Combine”, which is very similar to “List.Map” in theory. The only difference being that you can specify an argument for each variable in the function. In your case the function will be “List.AddItemToFront”. It needs two variables to work - an item to be added and a list to perform the action on. In your case each item in listA is the “item” variable and listB is the “list” variable.
Also note the “Flatten” node. Most functions won’t need it there, “List.AddItemToFront” is an exception due to the way the node works. For example “List.AddItemToEnd” doesn’t need it: