Install libgfortran-6-dev-x32-cross by entering the following commands in the terminal:
sudo apt update sudo apt install libgfortran-6-dev-x32-cross
Description:
Runtime library for GNU Fortran applications (development files)
This package contains the headers and static library files needed to build GNU Fortran applications.
Homepage: http://gcc.gnu.org/
Version: 6.4.0-17ubuntu1cross1
Section: universe/devel