Fixed straight distance between 2 SC

[Trainzland]

everyone,

I have 2 problems to calculate a straight fixed distance between 2 points on a spline.

1)
Point A (Spline Controller)  is moving.
Point B (Spline Controller)  should be recalculated by a fixed straight distance (or radius) to Point A.

[img][/img]

Code:

public SplineController pA;
public SplineController pB;
public float distance = 30;

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2) Another Points A and B. 
But Point A owns now a world position.
The Green Points are the result of (1)

[img][/img]

Code:

public Transform pA;
public SplineController pB;
public float distance = 20;

Would someone so kind and provide me with some lines of code how to. I'm not able to deal with vec math.
Thanks and kind regards,
Roger