The two coordinates' x variables are the same, while the y variables change. This means that it is reflected over the x axis. Reflecting over the y axis would cause a change in the x variable, as it would have to move sideways, so this can't be the case since the x variable stays as 4 even after the reflection.
10^-3 means move the decimal to the left 3 places. The negative means left, positive would mean right. We add 0 to make enough places to move it to the left 3