In the "sum" below one of the digits is missing, marked by a question mark. Clearly this is not an addition, subtraction or any normal sum. So what is going on?
57944
81039
87025
-------
75?36
What digit has been replaced by the question mark?
As usual you can post your suggested answers as a comment on this website, reply to the post on Facebook or Instagram, or retweet or reply on X (formerly Twitter) @quizmastershop.
Answer at 9.00 on Monday