y = -1 is a horizontal line going through "-1" on the y axis
Note that the point (1,2) is exactly 3 units of distance above the line y = -1
When we reflect across this line, the point (1,2) will just move straight down to exactly 3 units of space below the line y = -1. Since we are not shifting left or right, the x coordinate of our original point will not change. The y coordinate of our original point will now need to be reduced by 6(3 units down to get to the line of reflection and then 3 more down to get to the image location)
The coordinates of the image point will be (1, -4)
Now we need to do the same process with (1, -4) being reflected across y=1
Note (1,-4) is 5 units of distance below the line y = 1 , so we need to reflect the point upward so that the image point is located exactly 5 units of distance above the line y = 1 Again, the x coordinate does not change, and our final image coordinates are (1, 6)
I guess more simply stated, if you're just looking for the number in the green box it would be " 1 " .. Reflecting points across horizontal lines only result in changes of the "y" coordinate since there is no shift left or right.