Find difference at the bottom of writing (8)
I believe the answer is:
subtract
'find difference' is the definition.
(difference can mean the result of subtraction)
'the bottom of writing' is the wordplay.
'the bottom of' becomes 'sub' (I can't explain this - if you can you should give a lot more credence to this answer).
'writing' becomes 'tract' (tract is a kind of writing).
'sub'+'tract'='SUBTRACT'
'at' acts as a link.
Can you help me to learn more?
(Other definitions for subtract that I've seen before include "Knock off" , "Take one quantity away from another" , "Take away (a number)" , "Deduct" , "Remove" .)