I found an EPEL mirror that keeps previous versions of packages: https://mirror.umd.edu/fedora/epel/
You can either make this your default mirror for the EPEL repo, or you can manually download the previous versions of the packages from there and then run the yum downgrade. I downgraded to 2.16.1 and things are working for me in RHEL7.
Note that WeBWorK doesn't require libapreq2-devel to be installed. You would only need this if you needed to compile something from source that depended on libapreq. With that being said, if you have it installed it will need to be downgraded at the same time as the other packages as Justin mentioned.
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