The coordinate for A, B, C, and D: (Current coordinates)
A: (-1, 4)
B: (-5, 8)
C: (-5, 4)
D: (-4, 2)
Once we reflect acorss the y-axis the coordinates become:
A': (1, 4)
B': (5, 8)
C': (5, 4)
D': (4, 2)
In this situation the coordinates just become positive.
I hope this helps!