Why does a Backtick (`) Replace a Question mark?? (")
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Answer:
This is a backtick. A backtick is not a quotation sign. It has a very special meaning. Everything you type between backticks is evaluated (executed) by the shell before the main command (like chown in your examples), and the output of that execution is used by that command, just as if you'd type that output at that place in the command line.
Text between backticks is executed and replaced by the output of the command (minus the trailing newline characters, and beware that shell behaviors vary when there are NUL characters in the output). That is called command substitution because it is substituted with the output of the command. So if you want to print 5, you can't use backticks, you can use quotation marks, like echo "$b" or just drop any quotation and use echo $b.