I clearly do not understand how you are working it out. But please feel free to edify us.
I thought I had!
All you need to do is answer my rephrasing of the question:
If the outside air pressure is 992mb, how high are we above 1013mb?
... and then explain why you think that's a different question from the one posed.
I say again, your answer is based on the the 992mb pressure being at sea level ... whereas the question says that it is the pressure at aerodrome level.