Could u provide a pic of the prism?
A or B. its a 50/50 here. I can't really tell whats on the graph.
In plain and short, what's 2/3 of 7/8? well, is just their product.
Start the line at 3 on the y-axis (vertical). then go down two boxes and to the right three & make a mark at that point. keep going down two and over three until the end of the graph. then just connect the marks.