How do i detect if a npc humainoid is at 0?

I am making a game where you kill NPC. but i can not figure out how to write this.(The script is to give gold to me when i kill an npc) Located in startergui:

local player = script.Parent.Parent
local leaderboard = player:WaitForChild("leaderstats")
local currency1 = leaderboard:WaitForChild("Gold")

function onDied()
	print("Dead")
	currency1.Value = currency1.Value + 100
end

script.Parent.Parent.Workspace.TutPrac.Viking.Humanoid.Died:connect(onDied)

Thanks!

Its usually better to put the localscript into the Tool of the sword.

Try using a sword and use this script. (Put it into the tool)

Use this link to learn how to make a sword if you dont know. (Also needed for the "Hitmark" part in the script: How to make a sword

local hitmark = script.Parent.hitname --Let this be the part that damages the player 
--(May need to watch the tutorial provided above) 

local player = game.Players.LocalPlayer
local leaderstats = player:WaitForChild("leaderstats")

hitmark.Touch:connect(function(npc)
	if npc.Parent.Name == "Viking" and npc.Parent.Humanoid.Health == 0 then -- Checks if the NPC killed is named Viking and checks if dead
		leaderstats.Currency.Value = leaderstats.Currency.Value + 50 -- Adds currency
	end
end)

Im not that professional at scripting but this is what I know. Use the Output of any errors. If the output does not help however, it may give you an idea on what to do.