In 'Ch3ch2ch2cooh' there are 4 carbons.
That means the name of the compound will start with But
There is also a COOH, which means that the compound is a carboxylic acid. So the compound will end in anoic acid.
Add these two together and you get: Butanoic acid
(But + anoic acid = Butanoic acid)
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Answer
Butanoic acid