Not sure if you'll get this in time but here goes.
The main thing they're going to want to see at the interview is that you're passionate about design and not going to be wasting a place that could go to someone else who really wants it.
Show your work, be confident and enthusiastic and try to use as much design terminology as you can ('typeface' rather than 'font' for example).
As for the assessment, I never did one but I suspect anything related to key skills (reading, writing, maths) is more to identify where you may need help rather than to 'test' you. This is the case I've found with KS subjects anyway.