Extracting length value of a line

Hello everyone,
I just started to learn grasshopper for two weeks and I have a very beginner question so pardon me in the first place…
So I made circles with these Pframes as their base plane (Let’s call it SmallCircle not to confuse with the big outline circle), and all of the SmallCircles are of course have the same radius by default.
Now I want to make the radius of the SmallCircles based on the result of, let’s say, A divided by B whereas A is [Length from the outline circle’s divide point to the outline circle’s center point] and B is [Length from ‘that’ Pframe center point to the outline circle’s center point]; So that the closer the Pframe is to the outline circle’s center point, the bigger the SmallCircle’s radius will be…
Now, how can I get the ‘value’ of the length of A and B? (A is definitely the ‘Ln’ on the attached screenshot) so that I can use both values with division operator for the circle’s radius?
Thank you so much !

Expression component (add variables by zooming in to the +)

rounded to 2 decimal places

Is it used to divide X and Y (as I notice the “/” symbol) or is it used to get the length from X and Y ?

A is the distance between the start point and the frames and B is the distance between the frames and the end point