So first, you will have to find out how many words he types in 1 minute, so you divide 570 by 15 and then you'll get 38, so Sam types 38 words per minute.
Then, we know that 2 hours is equal to 120 minutes. So you multiply 38 by 120 because you want to calculate how many words Sam types in 120 minutes.
So your answer should be 4,560 words in 2 hours.
I hope this helped (: