I don't really know how to explain this, but I'll try...
For A2 English langauge (AQA), the c/w is 20%, so 80 ums, and the exam is 120 UMS, so 30% of the A-Level.
Do you need to get 90% UMS across the A2 exams (180 UMS), or an average of 90% across exams.
You could get 100% on the coursework, so 80 ums, but 80% on the exam, so 96 ums. That would give you 176 UMS, so not 90%, but you got 100% on one unit and 80% on the other, so that averages out on 90%. So which do you need to get an A*?
Sorry, is that clear?