Solving an Unfamiliar Derivation: Can You Help?

[Chocolaty]

Okay, I'm using this program called derive, and it usually tells me the steps to derive(duh) but it made a simplification which i don't understand. I'm sure it's just one of those things where i'll slap my own face when i'll know what it was, either that or throw up and roll around in my own bile...

How do you go from:
x·3·(x - 4)^2 + (x - 4)^3

to(the solution):
4·(x - 1)·(x - 4)^2

thanks to whoever answers
<3

 

[shmoe]

Remove the common factor of (x-4)^2 from the first line.