Here, we have a formula.
(-2, 8) is not some random two numbers. It stands for the x-coordinate and y-coordinate, where:
(x, y) = (-2, 8) OR x = -2 and y = 8
On the coordinate-plane, commonly known as a graph, the big horizontal line is known as x. The big vertical line is known as y.
Each little dash on the line represents a number. For example, A would be (2, 8) since you go right 2 "x" units and up 2 "y" units.
Thus for (-2, 8) it resides at point C, since you go left 2 "x" units and right 8 "y" units.
Remember, x is left and right, and y is up and down.