I can not find a solution to this question at all, anyone any ideas?

Find a unit vector that is perpendicular to both 4i + 10j - 3k and 5i - 9j + 7k

I am as far as finding the vector between them, i - 19j + 10k

I have called the new vector n1 i + n2 j + n3 k

Since they are going to be perpendicular n1 -19n2 +10n3 = 0

I am now stumped.

Thanks for your help.