Summary of Steps

Open a terminal window. Keyboard shortcut: ctrl-alt-t

Type the following on the command line then hit enter:

lsb_release -a

The text in the terminal window should look similar to this now:

xitalogy@ubuntux64-virtualbox01:$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.4 LTS
Release:	18.04
Codename:	bionic
xitalogy@ubuntux64-virtualbox01:$

The Ubuntu version number is displayed on the Description line.

lsb_release Options from Man Page

From the Ubuntu man page for lsb_release. Note -a for Display all of the above:

OPTIONS
       The program follows the usual GNU command line syntax, with long options starting with two dashes (`--').  A summary of options are included below.

       -v, --version
              Show  the  version  of  the  LSB  against  which your current installation is compliant.  The version is expressed as a colon separated list of LSB module descriptions.

       -i, --id
              Display the distributor's ID.

       -d, --description
              Display a description of the currently installed distribution.

       -r, --release
              Display the release number of the currently installed distribution.

       -c, --codename
              Display the code name of the currently installed distribution.

       -a, --all
              Display all of the above information.

       -s, --short
              Use the short output format for any information displayed.  This format omits the leading header(s).

       -h, --help
              Show summary of options.

To display the man page from the command line, type the following:

man lsb_release

Thanks to Pexels for the free image