I'm looking for an excel formula to figure how many 5-Star reviews would be needed to move a 4.3 average, from 361 reviews, up to a 4.6 average. I thought I had it figured out but it didn't work as other known volumes of existing reviews and average stars changed. I would like to just apply a formula to a sheet for all of my stores and all review sources. Input fields would contain the current number of reviews and current average stars (per review source). Result field would give the stores an idea of how many 5-Star reviews they need (per source) to bring up their score to my benchmark.

Yes, I did Google it. I didn't find anything that would fit this particular scenario. Can you assist?