Identify a mistake in each sentence and correct it

V. Identify a mistake in each sentence and correct it.
26. They are talking to financial problems.                                   _________
27. Mathematics are my favourite subject.                                   _________
28. Could you tell me how using this machine?                            _________
29. He arrived here ago five minutes.                                           _________
 30. He didn't met his girlfriend.                                                     _________

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