Unfortunately this formula would simply add all the numbers to the left of the cell ie. Probably add-ons are my next favorite feature. Just switch to Insert tab and click Equation Insert New Equation to toggle on Equation Tools.
Click the table cell in which you want to insert a formula.
If Word doesnt supply the formula for you enter SUMLEFT. You can click Write button and use your mouse or writing pad to write the formula here. Put the cursor in the cell that will hold the sum or product of the cells above below to the right or to the left. The next value we need to add is the flight number which is already there in the cell A2.