How to highlight cross point of two lines in a graph?

[TheoS]

Hi all,
I am sure it has been asked before but I can't find it in the forums.

I made a line graph with two lines A and B
Line A will cross line B where this is is depending on the values that create A and B
I want to mark this cross point with a dodand the text "payback"
How can I make this happen?
Hope to hear from you thanks in advance.

 

[Logit]

.
Hopefully this resources will assist :

https://chandoo.org/wp/2010/11/11/highlight-data-points-scatter-line-charts/