How to find a point along an vector at a variable distance

Question

I need to find the value along a vector for a given x coordinate. Like so;

I know the values of A, B and C. All of these value are variable. I need to calculate X.
I know this is possable I just can't remember my trigonometry lessons.
I'm aware of similar questions like this one but it only finds the mid-point.

Thank you.

Answer 1

Hint, Use similarity of triangles. i.e. $AC:CX = 100:100$