A. Cats with stopped up noses tend to eat much less, as you've noted, because they can't smell their food as well. And the smell of food is pretty important to a cat's appetite. You can start by warming up the food in a microwave - not too hot, test it yourself by putting your finger right in the center, as the temperature of microwave food can vary - as this will intensify the smell and hopefully make your cat more interested.
Saline nose drops, like those that are used on little kids, are safe to use on a cat to clean the discharge that is dried around and in the nose. There's a brand called Little Noses that's available in the U.S. That I like. You can put it on a q-tip and try to remove the debris. Humidifying the air with a humidifier can help as well, or you can put the cat in the bathroom and run the shower enough to generate steam. Don't use "real" nose drops like Neo-synephrine or anything else like that - cats quickly build up resistance to them.
A 3 oz can of food is an OK amount in 24 hours, but do try the techniques above to help your cat get more interested in food. You might also try some baby food - no garlic or onions in the ingredients - as cats usually really like the taste of it.
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