Adding quantities in column C if data in column A and column B are identical

One of options: formula in D4:

Formula:

Please Login or Register  to view this content.

and copy all the way down (double click on filling handle). Select column D, copy it and Paste Special as values.
Now filter whole range on column D equal "delete" and delete visible rows.
Disable filter and only summarized rows will remain.

If that takes care of your original question, please select Thread Tools from the menu link above and mark this thread as SOLVED.

Also, as a relatively not active member of the forum, you may not be aware that you can thank those who have helped you by clicking the small star icon located in the lower left corner of the post in which the help was given. By doing so you can add to the reputation(s) of those who helped.