Graph with a line going through points zero comma two point five and four comma two point five.
select the equation of the line that passes through the point (3, −1) and is perpendicular to the line on the graph.
y = −1
y = 3
x = −1
x = 3
: (

-- The points (0, 2.5) and (4, 2.5) are both 2.5 above the x-axis.

-- The line through them is a horizontal line.   Its equation is  y = 2.5 .

-- Any line perpendicular to it is a vertical line.

-- The vertical line through the point (3, -1) is the line    x = 3 .

The answer is part a: use