Distance between parallel planes?

[LaraCroft]

Homework Statement

How do I determine the distance between the parallel planes
2x-4y+ 2z = 5 and -2x+4y-2z= -9: ___?

Homework Equations

The Attempt at a Solution

I got 1/4, but I think that is wrong. Any help would be great!

 

[Dr.D]

Why don't you show how you got 1/4, and let's see what we can do to help.