How to find the new coordinates of a point, knowing the initial coordinates, direction and length of the line that the point will move to.
I searched in the documentation, but found only such a complicated way: I create a camera, set the direction, move the camera forward by a length, determine the camera coordinates.
Maybe there is an easier way? Help me please.

where start is your initial coordinates as a Vector3, direction is a unit Vector3, if not already a unit vector do direction.normalize(), distance is the length of the line and final is the final coordinates as a Vector3;

If you are moving a mesh you can use translate, eg