Adding totals for 2 line with Sumif

Right now I have a column and the formula looks like this.

=SUMIF('Running Totals'!N:N,'Inventory Sheet'!B3,'Running Totals'!E:E)

It works great and gives me the totals from E:E with the correct corresponding inventory names. How do I get this formula to add some other number from another column. Such as....

=SUMIF('Running Totals'!N:N,'Inventory Sheet'!B3,'Running Totals'!E:E) + ('Running Totals'!N:N,'Inventory Sheet'!B3,'Running Totals'!F:F)??

Essentially I am wanting to add E:E lines and F:F lines together to get one sum with the corresponding inventory ID.