My cat Arong has refused all food and water for 3 days; what should I do??

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My mother has a 25-year-old cat named Arong,
and I am so worried because he has refused all food and water for 3 days.
My mother is also unwell and hasn't been able to eat for 3 days,
and Arong just stays stuck right by her side, lying there without eating anything.
I'm thinking about buying some premium Hanwoo beef that he loves to see if he'll eat, but what should I do?