Reflection of a figure
If we want to reflect a point across y-axis, we should treat it as a mirror:
As we can observe, in order to reflect it we just must change the sign its x coordinate.
(x, y) ↔ (-x, y)
Then, if we wanted to reflect the point X, since its coordinates are (-5, -1)
we must change the sign of the x=-5:
X(-5 , -1) ↔ X'(5, -1)
Answer: X'(5, -1)