This will get you started. If you want more help, you'll need to put more effort into your question:

declare or otherwise obtain list of files
declare scalar for max (a, b) equal to undef

for every file{
  open the file
  for reach line{
    split the line into scalars (current a, current b)
    if current a > max a then set max b = current b
  }
  close the file
}

you now have b from the maximum seen value of a
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Update:
I'm not sure what the post has to do with hashes or hash files (I'm not even sure what is meant by a hash file), so my response didn't address that.