I primarily work with students in the following suburbs of Chicago:
Libertyville,
Vernon Hills,
Mundelein,
Lake Forest,
Lake Bluff, etc.
Honor's Geometry: Reflections Problem 13.5 #17: Libertyville
Here is the solution. The slope of the "fourth" line is -3/2, so the 2.5 as the y-coordinate of R is not an estimate from the diagram, but actually can be calculated algebraically by writing an equation of that line using two points, and then substituting x=9. But I think in this case it's sufficient to "figure it out" based on slope.
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Math and Physics Tutor for High School and College Students in Libertyville, Lake Forest IL, Vernon Hills, etc., and online