Question

What’s the correct answer??

Answer 1

Cosine of an angle is the adjacent leg divided by the hypotenuse. 

So cos(60) = a / 12

I'm going to assume it's your last option because it's not in the picture. 

Answer 2

Yes SOH-CAH-TOA, Cos= Hypotenuse+Adjacent, so, cos(60) a/12 would be the correct answer so D.