The picture: http://i55.tinypic.com/n324ip.png

The problem:

The pyramid above has altitude h and a square base of side m. The four edges that meet at V, the vertex of the pyramid, each having length e. If e=m, what is the value of h in terms of m

Question: The book i got this problem from already gives the answer (m/) but gives no explanation on how to solve it. I am having trouble finding a way to get that answer.

Help would be appreciated.