Chapter 3 - Linear and Quadratic Functions - 3.2 Building Linear Models from Data - 3.2 Assess Your Understanding - Page 136: 27

$y=-2x+3.$

We know that by the Slope Formula: if $P_1(x_1,y_1)$ and $P_2(x_2,y_2)$ are on a line, then the slope is: $m=\frac{y_2-y_1}{x_2-x_1}$. Hence here: $m=\frac{-3-5}{3-(-1)}=-2.$ Therefore: $y-5=-2(x-(-1))\\y-5=-2(x+1)\\y-5=-2x-2\\y=-2x+3.$