Answer
We see that the choice of coordinate system does not change the center of mass.
Work Step by Step
We use the equation for center of mass to find:
$x_{cm}=\frac{(80)(.75)+(50)(-.75)}{80+50}=\fbox{.1731 meters}$.
Comparing this to example 9.1 as the book asks us to do, we see that the choice of coordinate system does not change the center of mass.
