I understand it like this.
Your stood at an aerodrome which is 968ft above mean sea level. You have an altimeter in your hand. In order for it to read 0 then you must set 992mb.
Now, the question is asking for the aerodrome pressure altitude.
"pressure altitude is the indicated altitude when the altimeter is set to an agreed baseline pressure setting" In our case, this is 1013mb.
So, were stood at the aerodrome and it wants the aerodrome pressure altitude. So to set 1013 from 992 we need to go up 21mb. 21mb at 30ft per second is 630ft.
Now are we to believe because we have been given the QFE the altitude is 0, well yes.. Hmm interesting, whilst typing this out i actually understand what Islander is talking about...