# "Let the linear expression we need to add be:" \qquad L. #
# "So, from the question, we want" \ L \ "to achieve the following:" #
# \qquad \qquad \qquad \qquad \qquad \qquad \qquad \qquad L + ( -4 y + 2 ) \ = \ y. #
# \qquad :. \quad \ L + ( -4 y + 2 ) - ( -4 y + 2 ) \ = \ y - ( -4 y + 2 ) #
# \quad :. \ \ L + color{red}cancel{ ( -4 y + 2 ) } - color{red}cancel{ ( -4 y + 2 ) } \ = \ y + 4 y - 2 #
# \qquad :. \qquad \qquad \qquad \qquad \qquad \qquad \ L \ = \ 5 y - 2. #
# "This is our answer." #