Why do you have 2? If the EIN number in box b is the same and you work in more than 1 state or city, sometimes they will give you another W2 with the extra state information on it and the top part the same or not filled in. If this is the case, list one W-2 but include both state or local taxes on it. It will let you type in more than one line for boxes 15-20. Don't add the boxes together.
And TN doesn't have an income tax so leave all boxes 15-20 blank, no spaces for them.