For a relation to be considered a function, there must be only one output for every input, i.e., there must be only one value of y for every value of x.
Considering "the time" as the input and "the cost" the output, you can graph the relation as follows:
• As you can see, the parts of the relation do not overlap, this indicates that every value of x (input) has only one value of y (output) and therefore, it can be considered a function.
