I answered this same idea recently, let’s see if I can find it. Aha! This thread: (pertinent answer on other side of embed)
Basically, make an arc with a radius of the desired length centered on A40, intersecting the pertinent arc. Use “Point of intersection arcs” tool, (second tool down on the right of the Arc toolset,) to place the point. (ETA: “Point intersection curves” on the lower left of Curves toolset would work in more situations.) That should do it!
Best wishes! 