Line Chart - Highlight and Label Specific Point?

Hi all!

I am working with a Pareto chart but have a new request from my team. They want to have a data label/point where the curve hits 80% - the intersection of the two lines. BUT they don't want it to say 80% (y-axis), they want it to say 20% or 40% or whatever percentage (x-axis) makes up that 80%. Trying to find a way to do this using lines, measures, and points, but getting stumped.