Question

the point (2,-4) is reflected across the line y=-1. What are the coordinates of the image?

Answer 1

you can just add 1 to the y component of the point, reflect thru the y=0 axis, then subtract out the 1

Answer 2

another idea is just to assume y=-1 is the midpoint of the y values

(-4 + yo)/2 = -1

-4 + yo = -2

yo = 4-2