If you are dilating a coordinate (a, b) by the scale factor "z", the new coordinate will be (za, zb).
It simply means that we multiply each cordinate, x and y, by the scale factor given.
Here,
The coordinate is (1, -8) and hte scale factor is "5". Thus, we multiply each coordinate by "5". So, it becomes:
The image is at (5, - 40)