I have a question dealing with perpendicular vectors. In the book it states this;

10.Find a vector that is perpendicular to both given vectors.

a)u = [1, 2, 3], v = [3, 2, 1]

The answer I got was n = [1, -2, 1] but the book has it as a multiple of -4, which is [-4, 8, -4]. Why is it -4?