I need to install OpenMotif (because I need to use a graphics program, Grace, and lesstiff produces a crash with some of its functions)

My problem is making sure I have the right X11 bin, include and libs directories, since there are a number of X11 and X11R6 directories
:

"To unpack the distribution, create a directory to hold all of the sources
and untar everything into that directory:

% mkdir $MOTIFSOURCEDIR
% cd $MOTIFSOURCEDIR
If you
unpack the distribution, you will have the following subdirectory under
$MOTIFSOURCEDIR:

motif"



ok, so I made
/usr/OPENMOTIF

and put the tarball there. Unpacking it, there is the motif directory, so
so far so good

"Create a build directory that is not a subdirectory of the Motif master
source directory, for example:

% mkdir $MOTIFBUILDDIR

Create a symbolic link tree using the following command:
% lndir $MOTIFSOURCEDIR $MOTIFBUILDDIR

where $MOTIFSOURCEDIR is the Motif master source directory. Note that
the directory containing the lndir program must be in your $PATH.
Note that the builds described below must be done in the order given:"

ok, so
mkdir /usr/OPENMOTIFBUILD
lndir /usr/OPENMOTIF /usr/OPENMOTIFBUILD



"
1. Customize $MOTIFBUILDDIR/motif/config/cf/site.def to reflect local
preferences for install locations, compilers, paths, etc. Note that
the default install location is /usr/dt, and is probably not the one
you want. You should change it to where you want Motif to be installed,
probably /usr.


2. If you are building with imports (the default setup in site.def),
construct the necessary links as follows:

% cd $MOTIFBUILDDIR/motif
% mkdir -p imports/x11
% cd imports/x11
% ln -s <X11_bin_directory> bin
% ln -s <X11_includes_directory> include
% ln -s <X11_libs_directory> lib

"

Here is my problem. What directories do they mean?
/usr/bin/X11 is the bin directory? What should I look for to
know for sure which are the right directories(BTW, my installation is Slack 9)