Is the 4 in your desired output a typo? Or is there another rule you're only going to tell us after getting answers? Anyway, a one-liner, assuming your numbers are space separated: 
perl -anE '($s,$F[1])=($F[1],$F[1]-$s);say "@F"' <your-file>

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In reply to Re: subtracting two lines in file by JavaFan
in thread subtracting two lines in file by frank19

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