In a <em>function</em>, <u>one value of the input can be related to only one value of the output</u>.
In a graph, it means that for each value of x(horizontal axis), there can only be one respective value of y(vertical axis), that is, there cannot be point that are aligned vertically.
In this problem:
On the <em>first </em>graph, there are points that are aligned vertically, for example, when x = -2, y = -2 and y = 2, hence, it is not a function.
On the <em>2nd and on the 3rd graph</em>, there are no points aligned vertically, hence, they are functions.
Gary should be the correct choice because when you balance their checkbook correctly you should have a balanced or equal amount in both your check register and your bank statement.
Good luck! Please let me know if I have chosen the wrong answer. All though I am very confident in my answer.
