Chapter 8 - Coordinate Geometry and Linear Systems - 8.4 - Writing Equations of Lines - Problem Set 8.4 - Page 360: 5

$x+3y=20$

Using $y-y_1=m(x-x_1)$ or the Point-Slope Form, the equation of the line with the given point $( -4,8 )$ and slope $m= -\dfrac{1}{3} $ is \begin{array}{l}\require{cancel} y-8=-\dfrac{1}{3}(x-(-4)) \\\\ y-8=-\dfrac{1}{3}(x+4) \\\\ 3(y-8)=-(x+4) \\\\ 3y-24=-x-4 \\\\ x+3y=-4+24 \\\\ x+3y=20 .\end{array}