Translation refers to a rigid motion or transformation where you move an object from one location to another.
Translations are base on the rule (x,y) -- (x+a, y+b) where the words right and left represent the change in the x-axis, and the words up and down the change in the y-axis.
In this exercise it is asked you to find the coordinates of the preimage of point T', which has the coordinates (-3,4) and is the effect of a translation of 3 units up. As previous said, the words up and down represent a change on the y-axis, meaning that the y-coordinate is the one that should be changed.
If the translation from the preimage to the image was 3 units up, then the preimage can be found by subtracting three units.
Pre-image: (-3,4-3)= (-3,1)
The point that represents the coordinates of the pre-image is (-3,1).