Factoring Quadratic x²+bx+c with c<0

After a long time, Richard finally figures out that $f(x) = x^2-11x-840 = (x+24)(x-35)$. He still needs to factor $x^2+11x-840$. Even though Richard is really tired, he is able to figure the factorization really quickly.

Which of the following is the factorization of $x^2+11x-840$?