Refer to the figure shown below.
The transformation that maps ΔABC onto ΔA'B'C' is a reflection across the x-axis (or across the line y = 0).
When ΔA'B'C' is reflected across the line x = -2 (shown in the figure) to form ΔA"B"C", the vertex of ΔA"B"C" will have the same coordinates as B', which is (-2,-6).