How to make a NPC keep its distance from Zombies?

I need to make a NPC have its walkspeed set to 0 when it is close 20 studs or less to another NPC with its humanoid labeled "Zombie", so far I havn't managed to do it, if the NPC can walk away then it will be even better.

Do you want the NPC to walk away from the Zombie or have its WalkSpeed set to 0? Because the NPC can't really move if it has 0 WalkSpeed, if you want to set the Walkspeed to 0 then its really easy.

wait(1)

print('Script Loaded')


local NormalSpeed = script.Parent.Humanoid.WalkSpeed
function FindChild(pos)
	local ListOfObj = workspace:GetChildren()
	local Dist = math.random(20, 40)
	local Found = nil
	local IsHuman = nil
	local HumanPart = nil
	local Torso = nil
	for x = 1, #ListOfObj do
		Found = ListOfObj[x]
		if (Found.ClassName == "Model") and (Found ~= script.Parent) then
			IsHuman = Found:FindFirstChild("Zombie")
			HumanPart = Found:FindFirstChild("Torso")
			if (HumanPart ~= nil) and (IsHuman ~= nil) and (IsHuman.Health ~= 0) then
				if (HumanPart.Position - pos).magnitude < Dist then
					Torso = HumanPart
					Dist = (HumanPart.Position - pos).magnitude
				end
			end
		end
	end
	return Torso
end

while true do
	wait()
	local Dir_Pos = FindChild(script.Parent.Torso.Position)
	if Dir_Pos ~= nil then
		print 'Zombie was found!'
		script.Parent.Humanoid.WalkSpeed = 0
	else
		script.Parent.Humanoid.WalkSpeed = NormalSpeed
	end
end