1. which variable did you plot on the x-axis, and which variable did you plot on the y-axis? explain why you assigned the variables in that way.

If you talk of a scatter plot, regularly the x-axis is used to plot the explanatory variable, this is the possible cause; while the y-axis is used to plot the varibale that is being explained, the result, the efffect.

If you are dealing with a function or model, you the convention is to use the x-axis for the independent variable, this is the input, while the y-axis is for the output or dependent varibale (which is determined by the independent variable).