CFrame.Y cannot be assigned to?

So basically, I'm creating this double-jump script in which a part will appear on the bottom of the player's foot giving them a brief period to jump on that part.

Script:

--ServerScript inside of a part
script.Parent.Touched:Connect(function(hit)
	if hit.Parent:WaitForChild('Humanoid') then
		local touching = script.Parent:GetTouchingParts()
		local part = Instance.new("Part",workspace)
		part.Size = Vector3.new(1,1,1)
		part.Name = "hi"
		part.Anchored = true
		part.CanCollide = true
		part.CFrame = hit.Parent:WaitForChild('HumanoidRootPart').CFrame
		part.CFrame.Y = hit.Parent:WaitForChild('Humanoid').HipHeight - 2
		wait(.1)
		part:remove()
		for _, p in next, touching do
			print(p.Name.." is touching "..script.Parent.Name)
		end
	end
end)

The thing is, on line 11, it says: Y cannot be assigned to

Any help please?