One of the factors of WHAT is ?
Or are you asking how do you factorise ?
Assuming the problem really is "which of these 5 choices is a factor of this expression?", start with each of them and think what must be the other factor. For example, if one factor were 15x- 1, the other would be of the form ax+ b. (15x- 1)(ax+ b)= 15ax+ (15b- a)x- b so we must have a*15= 15, b*1= 4. In that case, is 15b- a= 17?
(And I agree with Prove It- please state the full problem in the first post. Don't make us guess what it is.)