@enyonam, if you don’t want to do it via server side query, you can also do it via front-end on your page.
#2. you just add a table header (i.e. <th>) for the static column name, and then add a new row (i.e. <td>) for the calculation with your formula. You can use the Data Formatter for the difference in date. You can refer from this post: Time posted
#3. also add another table header and another <td> for the calculation.