Depends on what you mean by "right." If the question is to factorcompletely, then Answer B would be better, because in the first factor of Answer A (5x - 10), you can factor out the greatest common monomial factor, which is 5. So

(5x - 10)(3x + 1) =

5(x - 2)(3x + 1)

... which is Answer B with the binomials swapped.