Installing Expansion Packs

Hello everyone,

I have read all the appropriate instruction manuals on how to install the expansion packs and I am having trouble on installing the University Life expansion pack. I created the .dmg image, I copied and pasted everything from the university life folder to the .dmg image and now I am trying to open the installer using stuffit but I keep getting an error that says "The StuffIt Engine was unable to determine the file format."

If anyone can help me, I would really appreciate it.

Also, I hope I put this topic in the right place, I'm new.

//EDIT: Never mind I think I might have figured it out.