Question

slope of one of the dotted lines: $\frac{1}{2}$
slope of the line of reflection:
try values

Explanation:

Step1: Dotted line slope is 1/2

Given slope of dotted line: $\frac{1}{2}$

Step2: Line of reflection is perpendicular

Perpendicular slope: $-\frac{1}{\frac{1}{2}} = -2$

Answer:

-2