Need help ASAP, returning to stock ROM

[FrostyGTA]

So I bought a used Transformer Prime from someone who neglected to tell me it's rooted with CM9, I absolutely want nothing to do with rooting or hacks or any of that crap. It's partially my fault for not going over the tablet before buying it but I need to return this thing to stock, just like it was from Asus.

Can anyone help me? I have absolutely no idea what I'm doing when it comes to this stuff lol