We need to reflect the given figure across the y-axis. Then, we need to write the coordinates of the original and the reflected large dot.
When we reflect a point across the y-axis, its y-coordinate remains the same, and its x-coordinate changes the sign:

The original coordinates of the large dot is: (5,3).
Thus, the coordinates after the reflection will be: (-5,3).
Doing the same with the coordinates of the other vertices and joining them, we obtain the reflected figure, as shown below: