How can I find the maximum climb angle of a propeller driven aircraft from a graph of vertical velocity against airspeed?
All you need to do is to plot vertical versus horizontal speed using the same scale on both axes. Then the solution is the point with the steepest angle from the origin of the graph.
Of course, it helps to do this in metric units. And to add a description to the axes of a plot. The solution can then be directly read from the graph.