On a coordinate plane, triangle A B C has points (negative 1, negative 1), (negative 2, negative 1) and (negative 2, negative 4). Triangle A prime B prime C prime has points (1, negative 1), (2, negative 1), and (2, negative 4). What is the equation of the line of reflection that maps the pre-image to the image? y = x y-axis x-axis x = 1