the transformation (x, y) → (x, y- 4) , means the x-coordinate remains unchanged, while the y-coordinate has 4 subtracted from it, for example
the points on the diagram
A(1, 5 ) → A'(1, 5 - 4) → A'(1, 1)
B(4, 5) →B'(4, 5 - 4) → B'(4, 1)
C(4, 3) → C'(4, 3 - 4) → C'(4, - 1)
D(2, 2) → D'(2, 2- 4) → D'(2, - 2)