There’s something missing from the question, because you need both an original location to move away from *and* a direction in which to move. It would seem that this is what’s tripping you up.

Then it is fairly straightforward. Take the unit vector of the direction vector, i.e. the version of it that has direction but a length of 1, multiply that by the length *d* - this gives you the direction and distance to move - then add that to the original location.