The correct answer is C. Often, the multiplication sign is dropped when obvious, and so [tex] 12n [/tex] means "twelve times n".
For the record:
[tex] n -12 [/tex] is the difference between a number n and 12
[tex] \cfrac{n}{12} [/tex] is the ratio between a number n and 12
[tex] 12n [/tex] is the multiplication between a number n and 12, it's the same as [tex] 12 \times n [/tex]
[tex] 12+n [/tex] is the sum between a number n and 12
