Answer: The variable in the vertical axis (or y-axis) is the output
The variable in the horizontal axis (or x-axis) is the input.
Step-by-step explanation:
Usually, a graph of a function y = f(x) is represented in an X-Y coordinate axis.
An X-Y coordinate axis is conformed by two perpendicular lines, one vertical (y-axis) and one horizontal (x-axis)
The vertical axis (or the y-axis) is the output, and the horizontal axis (or the x-axis) is the input.
This method will work almost always, as is standardized that the x-axis corresponds to the input, and the y-axis corresponds to the output.