Can't install RMagick 4.0.0. Can't find ImageMagick with pkg-config on Ubuntu 16.04

Trying to install pdfbeads on Ubuntu LTS 16.04 with the command $ gem install pdfbeads I'm getting the error message "ERROR: Can't install RMagick 4.0.0. Can't find ImageMagick with pkg-config"

Below between the separators is the corresponding stdout.

$ sudo gem install pdfbeads

Building native extensions. This could take a while... Successfully installed nokogiri-1.10.7 Building native extensions. This could take a while... ERROR: Error installing pdfbeads: ERROR: Failed to build gem native extension.

current directory: /home/enemem/.gem/gems/rmagick-4.0.0/ext/RMagick

/snap/bin/ruby -I /snap/ruby/172/lib/ruby/2.7.0 -r ./siteconf20200127-10722-yuiix4.rb extconf.rb checking for brew... no checking for pacman... no checking for gcc... yes checking for pkg-config... yes

ERROR: Can't install RMagick 4.0.0. Can't find ImageMagick with pkg-config

* extconf.rb failed * Could not create Makefile due to some reason, probably lack of necessary libraries and/or headers. Check the mkmf.log file for more details. You may need configuration options.

Provided configuration options: --with-opt-dir --without-opt-dir --with-opt-include --without-opt-include=${opt-dir}/include --with-opt-lib --without-opt-lib=${opt-dir}/lib --with-make-prog --without-make-prog --srcdir=. --curdir --ruby=/snap/ruby/172/bin/$(RUBY_BASE_NAME)

Checked the mkmf.log file but it containe the same info, verbatim.

Then I tried to use the command

$ pkg-config --modversion imagemagick

and got this output:

Package imagemagick was not found in the pkg-config search path. Perhaps you should add the directory containing `imagemagick.pc' to the PKG_CONFIG_PATH environment variable No package 'imagemagick' found

Following up on this suggestion I tried to find where imagemagick is on my system by running:

$ sudo locate -b '\imagemagick*'

and got the output:

/usr/lib/mime/packages/imagemagick /usr/share/app-install/desktop/imagemagick-6.q16:display-im6.q16.desktop /usr/share/app-install/desktop/imagemagick:display-im6.desktop /usr/share/bug/imagemagick /usr/share/cups/ppdc/imagemagick.defs /usr/share/doc/imagemagick /usr/share/doc/imagemagick-6.q16 /usr/share/doc/imagemagick-common /usr/share/menu/imagemagick /var/lib/app-info/icons/ubuntu-xenial-main/64x64/imagemagick-6.q16_display-im6.q16.png /var/lib/app-info/icons/ubuntu-xenial-main/64x64/imagemagick_display-im6.q16.png /var/lib/app-info/icons/ubuntu-xenial-security-main/64x64/imagemagick-6.q16_display-im6.q16.png /var/lib/app-info/icons/ubuntu-xenial-security-main/64x64/imagemagick_display-im6.q16.png /var/lib/app-info/icons/ubuntu-xenial-updates-main/64x64/imagemagick-6.q16_display-im6.q16.png /var/lib/app-info/icons/ubuntu-xenial-updates-main/64x64/imagemagick_display-im6.q16.png /var/lib/dpkg/info/imagemagick-6.q16.list /var/lib/dpkg/info/imagemagick-6.q16.md5sums /var/lib/dpkg/info/imagemagick-common.conffiles /var/lib/dpkg/info/imagemagick-common.list /var/lib/dpkg/info/imagemagick-common.md5sums /var/lib/dpkg/info/imagemagick-common.postinst /var/lib/dpkg/info/imagemagick-common.postrm /var/lib/dpkg/info/imagemagick-common.preinst /var/lib/dpkg/info/imagemagick.list /var/lib/dpkg/info/imagemagick.md5sums /var/lib/dpkg/info/imagemagick.postinst /var/lib/dpkg/info/imagemagick.postrm /var/lib/dpkg/info/imagemagick.prerm

Version of the imagemagick package on my system is 6.8.9.9

$ sudo apt search ImageMagick | grep installed

imagemagick/xenial-updates,xenial-security,now 8:6.8.9.9-7ubuntu5.15 amd64 [installed] imagemagick-6.q16/xenial-updates,xenial-security,now 8:6.8.9.9-7ubuntu5.15 amd64 [installed] imagemagick-common/xenial-updates,xenial-updates,xenial-security,xenial-security,now 8:6.8.9.9-7ubuntu5.15 all [installed] libgraphicsmagick++-q16-12/xenial-updates,xenial-security,now 1.3.23-1ubuntu0.5 amd64 [installed,automatic] libgraphicsmagick-q16-3/xenial-updates,xenial-security,now 1.3.23-1ubuntu0.5 amd64 [installed,automatic] libimage-magick-perl/xenial-updates,xenial-updates,xenial-security,xenial-security,now 8:6.8.9.9-7ubuntu5.15 all [installed,automatic] libimage-magick-q16-perl/xenial-updates,xenial-security,now 8:6.8.9.9-7ubuntu5.15 amd64 [installed,automatic] libmagick++-6.q16-5v5/xenial-updates,xenial-security,now 8:6.8.9.9-7ubuntu5.15 amd64 [installed,automatic] libmagickcore-6.q16-2/xenial-updates,xenial-security,now 8:6.8.9.9-7ubuntu5.15 amd64 [installed] libmagickwand-6.q16-2/xenial-updates,xenial-security,now 8:6.8.9.9-7ubuntu5.15 amd64 [installed] perlmagick/xenial-updates,xenial-updates,xenial-security,xenial-security,now 8:6.8.9.9-7ubuntu5.15 all [installed,automatic]

Can anyone help?