This is a classic optical illusion puzzle involving perspective. Here's how you can work it out:
Firstly, the image is designed to make it seem as if the bars are in a straight line and their tops are aligned in a flat plane. Due to the perspective given, we can assume that if all the bars were to continue until they reach the ceiling, their tops would all align.
Given that the green bar is 3m high and reaches the base of the blue plane (presumably the "ceiling" in this perspective), we can infer that the point where the black and red bars appear to align must also be at the same height – 3m above the floor.
The grey-colored bar appears to continue beyond until it meets the blue plane at 4m high. However, with the optical illusion, the assumption is that if the red bar were to continue, it would meet at the same height. Therefore, the red bar is the same height as where the gray bar meets the blue plane, which is 4 meters.
So, the height of the red bar, according to this optical illusion and interpretation, would be 4 meters tall.