Chapter 6 - Section 6.8 - Exponential Growth and Decay Models; Newton's Law: Logistic Growth and Decay Models - 6.8 Assess Your Understanding - Page 488: 30

$y=-1.5x+7.$

By using the slope formula, $m=\frac{y_2-y_1}{x_2-x_1}=\frac{-5-1}{8-4}=\frac{-6}{4}=-1.5.$ We know that if the slope of a line is $m$ and contains $P_1(x_1,y_1)$, then its equation is: $y-y_1=m(x-x_1).$ Hence here: $y-1=-1.5(x-4)\\y-1=-1.5x+6\\y=-1.5x+7.$