Risk is zero and minimum profit is 10 point or maximum profit is open
When stock price move above 935 Square off your 900 strike put and carry on 840 strike put
When stock price move bellow 860 then square off your 840 put and carry on 900 strike put or cover your all position.
:- So if you are interested you can trade this option strategy.
Note :- For more info about this trade open this link and seen.