Using data in the excel file TD6_NFA, compute the following variables for the US and China over the period 1981-2015 (in millions USD and in \% of GDP): Total Foreign Assets (FA), Total Foreign Liabilities (FL) and Net Foreign Assets (NFA). Using data in the excel file TD6_NFA, compute the following variables for the US and China over the period 1981-2015 (in millions USD and in \% of GDP): Total Foreign Assets (FA), Total Foreign Liabilities (FL) and Net Foreign Assets (NFA)