"Simple interest" means the interest goes into a separate bucket, and it just waits there for you to come and get it. It <em><u>doesn't</u></em> get added to the amount in the account, so next year, you don't get interest on the interest.
4 percent of $2000 is (0.04 x 2000) = $80 .
That's how much interest you get each year.
At the end of 4 years, you have (4 x $80) = <u>$320</u> in the interest bucket. (And of course, you still have the original $2000 in the account.)