Chapter 3 - Parallel and Perpendicular Lines - 3-8 Slopes of Parallel and Perpendicular Lines - Practice and Problem-Solving Exercises - Page 202: 20

$$y-0 = -2(x-4)$$

We know that if the slope of two lines are opposite reciprocals, they are perpendicular. Thus, we find the opposite reciprocal of the given line and plug in the given point into the point-slope equation for a line, which is: $$y_2-y_1=m(x_2-x_1)$$ This gives: $$y-0 = -2(x-4)$$