I just saw the request for obtaining areas of multiple objects by BASAM YOUSIF on the current Wish List ballot. Until that wish is granted, here's a tip:
Convert your multiple closed polylines to regions using the REGION command.
Combine your multiple regions into a single region by using either the UNION command to add or the SUBTRACT command to subtract.
Use the LIST command to view the resulting total area.
Finally: If you want to "see" your area, use the RENDER command as a visualization tool.