How do I convert hex numbers to decimal ?

[bolega]

I have a bunch of related questions, but the solution is desired in
emacs lisp and to work inside emacs only.

1) How do I convert hex numbers to decimal ?
2) How do I convert ascii to the character that it represents, short
of a table ? Any function or simpler algorithm ?
3) What are the variables and how to set their values ?

read-quoted-char-radix
quoted-char-radix

4) How do i find the emacs lisp code for C-x = to see how it gives the
ascii of the char at the cursor and then use to find the reverse, ie
ascii to char ?

Thanks a lot to the star who can explain.