We perform the reflection across y=x first. This reflection switches the x- and y-coordinates; this maps:
A(2, 4)→A'(4, 2)
B(4, 4)→B'(4, 4)
C(3, 2)→C'(2, 3)
D(1, 2)→D'(2, 1)
Next we perform the translation. This translation shifts the figure 1 unit left and 2 units down, by subtracting 1 from the x-coordinate and 2 from the y-coordinate. This maps: