/usr/lib/libplasma_applet-system-monitor.so.4 is in plasma-widgets-workspace 4:4.8.2a-0ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libplasma_applet-system-monitor.so.4.8.0
/usr/lib/libplasma_applet-system-monitor.so.4.8.0