water coming up clogged bath drain?????

My 2nd story bath tub drain is clogged. If I fill the bathroom sink up with the stopped in place and then let the water drain out of the sink more water (and other mucky looking stuff) comes up the bath tub drain.
Yes, I live in an older home and no, I don't have a clue about plumbing.
Any suggestions?

Hire a licensed plumber or drain cleaner to remove the obstruction; it is affecting more than one fixture so that dictates the clog is farther away from the tub.

Magic in a bottle doesn't exist. (Liquid Drain Cleaner)