The given trinomial can be factored using factorization as
x²+19x+84
=x²+12x+7x+84
=x(x+12)+7(x+12)
=(x+12)(x+7)
Thus x+12 and x+7 are the factors of the given trinomial. From these we can see x+12 is listed in option A.
So the answer to this question is Option A