Help achieving task

[Rrabbit]

Hi there,

I have been set a task in excel but I have no idea how to approach it, my mind has gone blank. The dataset is fairly large.
It asks that I ...

Please combine the data on the two tabs, noting your steps to explain later.
Add a column of total score per respondent and grade per respondent (including showing formulae) - grade boundaries below

Grade boundaries per total score
Grade A >75%
Grade B 60-75%
Grade C <60%