Which glide reflection describes the mapping abc def (x, y) (x, y – 6) and reflected across y = 0 (x, y) (x, y – 6) and reflected across x = 0 (x, y) (x – 2, y) and reflected across x = −1 (x, y) (x, y – 6) and reflected across x = −1

As you can see in the figure attached, the vertex E is shifted 6 units down from the vertex B and it has the coordinates (1,-1).  
 If you draw the line x=-1 you will notice that the vertex B is 2 units left from the line and the vertex E is 2 units rigtht from the line.
 So, if you shifted the triangle ABC 6 units down and then you reflect it across x=-1, you will obtain the triangle DEF.
 Therefore, as you can see, the answer for the exercise shown above is:
 (x, y) (x, y-6) and reflected across x=-1