/usr/share/calc/help/prompt is in apcalc-common 2.12.4.4-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 | NAME
    prompt - display a prompt and wait for input from terminal
SYNOPSIS
    prompt(str)
TYPES
    str		string
    return	string
DESCRIPTION
   When prompt(str) is called and input is from a terminal, the string
   str is displayed and execution is halted until a newline ends a line
   read from the input; the string formed by the characters in the line
   (other than the newline) is returned as the value of prompt().
EXAMPLE
    ; x = prompt("? ");
    ? 273
    ; x
	"273"
    ; for (;;) {s = prompt("? "); if (s=="end") break; print "\t":eval(s)^2;}
    ? 3
	    9
    ? 2 + 3
	    25
    ? end
LIMITS
    none
LINK LIBRARY
    none
SEE ALSO
    fgetfield, fgetline, fgetstr
## Copyright (C) 1999-2006  Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
##
## @(#) $Revision: 30.1 $
## @(#) $Id: prompt,v 30.1 2007/03/16 11:10:42 chongo Exp $
## @(#) $Source: /usr/local/src/cmd/calc/help/RCS/prompt,v $
##
## Under source code control:	1995/12/18 12:34:58
## File existed as early as:	1995
##
## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
 |