The question doesn't seem complete, but let's work with what we have. I'm assuming the question is whether or not renee has enough prizes.
400 students x 2 prizes each = 800 prizes needed.
She has 50 boxes x 20 prizes per box = 1000 prizes in total.
So yes, she has enough prizes to give each of the 400 students 2 prizes each. She will have 200 leftover prizes.