Running count of matching numbers (or text)

Hello! I fear this may be a simple question, but I don't know how to phrase it correctly to find an answer.

I cannot figure out how to calculate a running count for a row of items that have duplicates. I've attached an example. I'm trying to calculate the highlighted row. I'm trying to get pivot tables to do it for me, but using the Running count function I just get a bunch of 1s.

Any help is appreciated!