Answer
The answer is below.
Work Step by Step
There are equal amounts of the object on either side of the y-axis. Thus, we see that the x center of mass is 0. We now find the y coordinate of the center of mass:
$y_{cm} = \frac{my_1 + my_3}{4m} = \frac{y_1}{2m}= \frac{\sqrt{3}L}{4}$
