Let Y be a subspace of X. If A is closed in Y and Y is closed in X, then A is closed in X.
First are there 2 cases to consider? (1) A is a proper subset of Y (2) or does this not matter?
Anyways, all I have is this:
Since A is closed in Y, is open in Y. Likewise, is open in X.
I am not sure what to do next.