Calculate the gravity value for trade between US and other countries. For this purpose, you can pick your favorite product from the list (there is plenty if you look up HS-4). If you do not have a favorite product, you can use HS-DDMM for the purpose, where DD stands for the date of your birth and MM stands for the month. Download the import and export data by county in an excel spreadsheet for 2018. Find the distance between each country and using formulas in excel spreadsheet, calculate the gravity value. For simplicity, assume n=1. Plot the value of trade (Y axis) against the gravity value (X-axis). What pattern do you observe? Explain the implication of such pattern.