Okay, if a company sold merchandise on account for $9,000 and then had $840 of it returned but paid the customer back in cash instead of just crediting Accounts Receivable, how would you enter that in the general journal or post to T-accounts (either answer will do)??

Even if something which happened seems "weird", it doesn't change what happened. If you get a return and give them cash, you still have to debit the sales returns and credit cash. The cash was indeed paid whether it should have come out of receivables or not. The entry has to reflect what actually happened.

I have serious doubts that a homework problem would have a customer getting a cash refund if they hadn't paid their receivable yet. So I'm suspecting the customer already paid the entire bill, then returned the merchandise, at which point the only thing you can do is a cash refund.