How to check if a row in Datatable A exists on Datatable B and remove it?

As the topic says, I have two datasets A and B.
I need to subtract from A the rows that exist on B. I know it's something simple starting with a
foreach (DataRow row in optouts.Rows)

and I've seen the various methods for 
tb.Rows.Find and tb.Rows.Remove but I can't figure it out...
Any suggestions?
Thanks!

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