If I have 12 (indistinguishable) plain cookies and 1 chocolate chip cookie, how many ways can I put the cookies on my Grandma's 4 x 3 tray? The most cookies you can put on it is 12.
We can put the 1 chocolate chip anywhere = 12 ways
Since the plain are indistinguishable.......they don't matter
So.....12 different ways