how to find out the apache version installed in ubuntu?
Open the terminal and type:
apache2 -v
-v Print the version of apache2, and then exit.
From the terminal you can enter
apachectl -v
or to get even more compile info on Apache enter
apachectl -V
of course as mention by @karel you can also use apache2 instead of apachectl... just giving an alternative. This worked for me in Ubuntu 18.04 and I'm using Apache 2.4.37.