A little bit of mathematics could help; the result you currently have is "number of days" (and it is a decimal number). In order to get "hours", extract digits behind the decimal point and multiply it by 24 (24 as "number of hours in a day"). Of course, digits in front of decimal point will still represent number of days.
SQL> select trunc(sysdate) - to_date('17.11.2008 13', 'dd.mm.yyyy hh24') res
2 from dual;
SQL> -- 1.4583333 => 1 = number of days (1 day)
SQL> -- => 0.4583333 = number of days (to be converted to hours)
SQL> select 0.45833333 * 24 hours from dual;
SQL> -- due to rounding issues, it is, actually, 11 hours
SQL> -- so, the final result is 1 day and 11 hours
I'll leave coding to you; feel free to present your code to the rest of the community (even if you don't succeed and need further help). However, I don't feel like doing your homework (at the moment, that is).