Chapter 4 - Section 4.2 - Building Linear Models from Data - 4.2 Assess Your Understanding - Page 290: 27

$y=-2x+3.$

By using the slope formula, $m=\frac{y_2-y_1}{x_2-x_1}=\frac{5-(-3)}{-1-3}=\frac{8}{-4}=-2.$ We know that if the slope of a line is $m$ and it contains $P_1(x_1,y_1)$, then its equation is: $y-y_1=m(x-x_1).$ Hence here: $y-5=-2(x-(-1))\\y-5=-2(x+1)\\y-5=-2x-2\\y=-2x+3.$