Saved search add up values of the same row

Hello everybody,

Within a saved search I would like to add an additional column which displays the sum of other columns of the same row.

Here is a screenshot of the first row of my saved search:

What I want to do is to add up the values of columns Sales Amount, Invoiced Amount and Return value and display the result in the column 'Sum of Order Book'

So the formula would be:

Sales Amount + Invoiced Amount + Return value = Sum of Order Book

So in the column 'Sum of Order Book' in my example should be the value

0.00 + 1 024.15 + 0.00 = 1 024.15

Can anybody help me with this formula?