/usr/lib/libqwtmathml.so is in libqwtmathml-dev 6.1.3-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libqwtmathml.so.6.1.3.abi1
/usr/lib/libqwtmathml.so.6.1.3.abi1