The last figure seems broken; some of the widget adjusters do not work (at least for me).
Other feedback:
I'd like you to prettify the figures so that I can substitute them for the ones currently in my lecture notes; like, get rid of the gray background, add proper labels, etc. Ultimately the goal is to turn all my notes into self-contained Jupyter notebooks, so I want to do this for all of my figures.
Please minimize the code cells (double click on the bar to the left of the code to turn it into three dots).
Added a graph for the PAYG system.