How to find a specific number from 2 columns

erictabak You mentioned that your example is just a simplification of the real problem. By doing so, you may get the answer to your question, which, most likely is not going to be the solution to your problem. Based on your description alone, I would first think of a simple pivot table, counting the number of occurrences of each number per source. It's difficult to imagine that you really want 6000 rows with sentences like in your example with sources that probably aren't just "a" and "b".

Alternatively, I would go for Power Query, to avoid great numbers of complicated formulae. It's demonstrated in the attached file. But, of course, based on your simplified example.