Learners doubt in LISP

[Rajsekar Manokaran]

I have just started learning lisp.
I use emacs (which was my motivation to learn LISP) to compile things.

There is a function in emacs called completing-read which when passed some
strings allows the user to select one string out of the many passed. I want to
allow the user select a string and then use the data associated with the
string.

eg.

(completing-read "Input: " '(("hai" 10) ("bye" 20)) nil t nil)

reads allowing completions hai and bye.

the nil t nil are insignificant (t - only allow things on the list).

Now this thing seems to return "bye" or "hai"
How do I access the 10 or 20 that comes together with it?

Thanks in advance.

M Rajsekar