It is a bit strange because latest Baculum 7.4.4 in the stable
packages repository for Ubuntu 16.04 doesn't contain PHP 5
dependencies. I think that you are trying to install an older version
than 7.4.4 or you use other repository than the official.
simple "apt-cache policy baculum" should show you which repository the "baculum" package is being installed from.
and "apt-cache showpkg baculum" will list its dependencies.
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