When plotting research data, X-axis(or horizontal axis) usually used for independent variable and Y-axis is used for the dependent variable. In this case, Heather wants to know how much earning on different numbers of hours. The dependent variable is the earning and the independent variable is the hours, so you put hours on the horizontal axis.
You want to make a 10x10 grid of data and the hours ranged between 1-10. If you plot them equally, approximate scale will be: (10h-1h)/(10)= 0.9h/grid
The closest option is 1 hour per grid. It will provide the best visualization since it won't stretch or minimize the data too much.
