On one file, you have the fuel surcharge for each domestic shipment your company made over the last four years. It includes the date, the weight of the package, the distance the package traveled, and the fuel surcharge for that shipment. On another file, you have average US diesel prices each day over the last three years. You want to understand the relationship between diesel prices and the fuel surcharge you are paying. In building a tidy dataset, please describe (in detail) the kind of join you need to perform in order to bring this information together.