Shortest distance

Point me in the right direction with this problem since I have no idea on how to tackle it.You're given 4 set of coordinates in R^3 that form a tetrahedron, then another 4 set of coordinates in R^3 that form another tetrahedron.
How do I find the smallest distance from the surface of one tetrahedron to the other?

>>12
My initial idea was to just calculate all the surface to surface distances. Which would give me 16 (4 for each surface) of them and pick the smallest one.
I thought that if I found all the surface to surface that already included all the other combinations since technically the vertexes and edges are part of the plane that contains the surface of the tetrahedron.
But I forgot how to calculate this.