Add Thick Border between Specified Rows, when Criteria Changes

Hello, have a quick one here where I need to add a thick bottom border between rows where the "grade" changes. So when a value in column B is different from the value above, there should be a thick bottom border added to the full row. This allows for sectioning for the eyes between "grades."

The attached shows a before and after sample on subsequent tabs. Thanks for any assistance!

Sheryl