Of course, it is not known precisely how many languages were spoken by Native Americans before Europeans reached the Americas. There are also differences as to what constitutes a language, as opposed to a dialect. Different scholars have different definitions and estimates. Therefore, it is probably a good idea for you to check in your text book or your lecture notes to make sure what figure your instructor wants you to give.
Estimates for the number of languages spoken vary widely. There are scholars who estimate that the number was as low as 300. At the same time, there are those who argue that up to 1,000 languages were spoken. There is simply no way to know for sure and so we must go with estimates rather than with solid figures.