Overall rating based on an alphabetical score

Hi Guys

I'm trying to come up with a document for our consultants to show them their overall ratings for the last 6 months.

They have 3 tasks to which targets are given, if they achieve, over achieve, did not meet targets they get a rating of A,B,C or D.

I need to know how to calculate their overall rating for the 3 scenarios, so if they scored an A, C and D, what is their overall rating?

I have attached a workbook.

Thanks!