Answer:
P'(-2, -2)
Explanation:
You want to know the location of P(-2, 4) after it is reflected in y=1.
Reflection
The image point will be as far below the line y=1 as point P is above the line. The x-coordinate is unchanged.
P is 4 -1 = 3 units above the line y=1.
P' will be 3 units below the line y=1, so its y-coordinate is 1 -3 = -2.
The image point is P'(-2, -2).
__
Additional comment
Reflection in the line y=k is described by the transformation ...
(x, y) ⇒ (x, 2k-y)
P(-2, 4) ⇒ P'(-2, 2(1) -4) = P'(-2, -2)