* How: This is an interrogative adverb, not a noun.
* many: This is a quantifier, not a noun.
* nouns: This is the word we are looking for! It's a noun.
* are: This is a verb.
* in: This is a preposition.
* the: This is an article (a type of determiner).
* sentence: This is another noun!
* before: This is a preposition.
* you: This is a pronoun, not a noun.
Therefore, there are two nouns in the sentence: "nouns" and "sentence".