I have not done these for a long time so don't expect me to be correct all the time.
So you want to find out 2.1% out of the 16,000 gifts. Then you will want to move the decimal (2.1%) to the left twice. You will get .021 . Once you get that, you will want to multiply that with 16,000. Once you did that, you will get your answer.
They can expect 336 gift to be exchanged