(0,2.5)(4,2.5) are the coordinates.
You will see that the y's are alike, which means this is a horizontal line and y will always be 2.5.
In this case, you might need a perpendicular line that is going through (3,-1)A perpendicular line would be a vertical line and a vertical line is signified by x = a numberso look at the points (3,-1)....what number is in the x spot ? It is 3 so the perpendicular line is : x = 3