On an x-y coordinate plane, x-values project a vertical line and y-values project a horizontal line. In this problem, you have been instructed to find a horizontal line and thus an equation in terms of y.
The standard form of a coordinate pair (in rectangular form) is (x, y). The given ordered pair (2, 3) shows the y-value as 3.
Therefore, the correct answer is 4) y = 3.