Thanks you guys, I was stuck. For your information, the solution for Level 25 shows the picture for Level 24, too. I take it that it is an accident and maybe you want to fix that.
Keep up the great work!
My husband wrote a program to find the solutions to each level. I'm not sure how to find where the secret levels are, but if someone can direct me there, I can get the solutions to the rest.
@Reton8 - Any way I can get the walkthrough achievement also?