We are asked to complete the following sentences:
Where we are told that the energy usage (measured in kilowats is a function of time of usage.
Therefore, in the sentence:
Identify the functional relationship between the variables: Energy usage is a function of time.
(where the words to complete are marked in bold)
In the sentence:
The graph of the function will show energy usage on the VERTICAL axis and time on the HORIZONTAL axis.
Warning, depending on your teacher, you may be asked to use ""y-axis" instead of vertical axis, and "x-axis"instead of horizontal axis.