You have a point with coordinates A(-6,1).
You have to determine the coordinates of a new point A' after a reflection over the line y=-x.
In order to find A' you consider the following rule:
The reflection of a point (x,y) over the line y=-x is the point (-y,-x)
Thus, you have:
x=-6, y=1
A(-6,1) => A'(-1,-(-6)) = A'(-1 , 6)
Hence, the coordinates of point A is A'(-1,6)