Answer: B' (x-4,y)
Explanation: A figure which is moved from one location to antoher, without changing its size, shape or orientation, is a figure that went through translation.
So, when a point is translated, it means it changed its position.
Point B has x- and y-coordinates: B(x,y)
Point B' after being translated 4 units left means:
(x,y) → (x-4,y)
In other words, translated point B has coordinates
B(x-4, y)
Because moving left is saying the point is moving towards the negative "side" of the x-axis.