The first thing you need to do is make a unit vector (a vector of length 1) that points in the direction of u, let's call it vector u'. To do this, simply divide u by its magnitude-- in other words, u' = u/||u||.
||u|| = sqrt((4)^2 + (-4)^2) = sqrt(32) = 4sqrt(2)
So, u' = <4,-4>/4sqrt(2) = <1/sqrt(2),-1/sqrt(2)>
Since this vector has length one and points in the direction of u, we can just multiply it by 3 and we will have a vector of length 3.
Thus, v = 3u' = 3<1/sqrt(2),-1/sqrt(2)> = <3/sqrt(2),-3/sqrt(2)>
I hope my answer has come to your help. Thank you for posting your question here in Brainly. We hope to answer more of your questions and inquiries soon. Have a nice day ahead!