Minecraft zombie visible range (bedrock)

Im working on a Minecraft map similar to a 3d Mario game. I am currently struggling on enemy AI and would like some help. I want to make it so when you are within the 16 blocks of a zombie, they act and move normally, but if you aren’t within their range they receive slowness making them unable to move. If it is possible I would like to make it so every zombie has its own system (example: if I was by a zombie, only that one would unfreeze, every other zombie would still be frozen.

Thanks everyone!